12 · 2017. 2. 28. · the angle kappa has also been referred to as the angle lambda in the older...

C H A P T E R 12Examination of thePatient—II

MOTOR SIGNS IN HETEROPHORIAAND HETEROTROPIA

Inspection of the Eyes andHead Position

Inspection of the Lids and LidFissures

When examining the eyes, attention should begiven to the lid fissures, their width, and theirdirection, by means of an imaginary line connect-ing the inner and outer canthus. If the two lidfissures are different in width, the possibility ofptosis or pseudoptosis of the upper lid with thenarrow lid fissure must be considered and the twoconditions differentiated.

A weakness of elevation of one eye will causethe lid fissure to be narrower than that of theunaffected eye. The patient may have true ptosisof the upper lid, especially if the superior rectusmuscle is involved. However, the lid may onlyappear to be ptotic as a result of narrowness ofthe lid fissure caused by the hypotropic positionof the globe (Fig. 12–1A). This is known as pseu-doptosis and can be established by having thepatient fixate with the affected eye (Fig. 12–1B).If pseudoptosis is present, the lids will open totheir normal width. The lids of the unaffected eyewill widen abnormally as the elevators of that eye

168

receive excessive innervation according to He-ring’s law (see p. 64), and the left globe movesinto a hypertropic position.

To correct a pseudoptosis, the only requirementis that the eyes be brought to the same level byoperating on the appropriate extraocular muscles.Any operation on the levator muscle of an eyewith pseudoptosis is a serious mistake. One shouldalso ascertain whether the width of one lid fissurechanges when the patient moves the eyes to theright or left, as in retraction syndrome (see Chap-ter 21), when the jaw is moved, or when thepatient speaks or chews, as occurs in the jaw-winking phenomenon of Marcus Gunn.

In infants the epicanthus frequently is more orless pronounced with a semilunar fold of skinrunning downward at the side of the nose and itsconcavity directed toward the inner canthus.39 Theepicanthus varies considerably in width and mayapproach and obscure the inner canthus, whichmay create the appearance of esotropia when noneis present (Fig. 12–2A). This is a common causeof pseudostrabismus. In time, the bridge of thenose develops, and in whites the epicanthal foldnormally disappears. The examiner may demon-strate to anxious parents that pseudostrabismusdisappears by lifting the skin from the nasal bridge

Examination of the Patient—II 169

FIGURE 12–1. Pseudoptosis in a patientwith right hypotropia caused by a pareticright superior rectus muscle and second-ary left hypertropia. A, Patient fixatingwith left eye; apparent ptosis of right up-per lid. B, Patient fixating with right eye;lid fissure wide open. Left hypertropia.

(Fig. 12–2B). Mongoloid and antimongoloid posi-tions of the lid fissures are occasionally observedin patients with the A and V patterns of strabismus(see Chapter 19) and should alert one to the pres-ence of such patterns.

FIGURE 12–2. Pseudostrabismus. A, A prominent epi-canthus may obscure some or all of the usually visiblenasal aspects of the globe, thus giving the false impres-sion that esotropia is present. B, For explanation, seetext. (From Noorden GK von: Atlas of Strabismus, ed. 4.St Louis, Mosby–Year Book, 1983, p 29.)

Position of the Globes—AngleKappa

The best means of estimating the relative positionof the eyes is to have the patient fixate a penlightat near vision and then at distance while the lightis held so that reflections from the cornea can beobtained. If reflected images from the two corneasappear centered under both conditions, one canassume that the eyes are properly aligned in dis-tance and near fixation. Estimation of the angle ofstrabismus by fixation on a light should be usedonly when examining uncooperative patients orinfants too young to sustain fixation of an accom-modative target at near, since the state of accom-modation is uncontrolled with this method.

Unusually narrow or unusually wide interpupil-lary distances should be noted. Narrow ones maycreate the impression that an esotropia is present.Of course, actual heterotropias may coexist withabnormal interpupillary distances.

Facial asymmetries also may create the impres-sion that a hypertropia is present. In such instancesthe lid fissure and the whole eye may appear tobe higher on one side than the other. However,further examination will reveal that, contrary tothe impression given by the patient’s appearance,there is no hypertropia, or a hyperphoria mayactually be present in the eye opposite the onethought to be involved.

Gross manifest deviations in primary positionare readily detected by inspection. However, smalldeviations may escape detection, or the presenceof a deviation may erroneously be assumed toexist because of the presence of a large anglekappa. An angle kappa is caused by failure of thepupillary and visual axes of the eye to coincide

170 Introduction to Neuromuscular Anomalies of the Eyes

(Fig. 12–3). The pupillary axis is the line passingthrough the center of the apparent pupil perpendic-ular to the cornea. The visual axis (or the line ofsight) connects the fovea with the fixation point.74

The angle kappa is formed at the intersection ofthese two axes at the center of the entrance pupil.The angle kappa has also been referred to as theangle lambda in the older literature.48; 53, p.80 Thevisual axis does not always coincide with theoptical axis (defined as the line connecting theoptical centers of cornea and lens) with which itforms the angle alpha at the nodal point and theangle gamma at the center or rotation of the eye.All these angles are geometric constructions (Fig.12–4), and only the angle kappa can actually bemeasured and is of practical importance.

As a rule, the pupillary axis touches the poste-rior pole of the globe slightly nasal and inferiorto the fovea. As a result, when an eye fixates apenlight, the reflection from the cornea will notbe centered but will be located in a positionslightly nasal to the center. This is termed a posi-tive angle kappa (Fig. 12–5). The student mayfind it helpful to remember ‘‘positive to nose.’’ Asufficiently large positive angle kappa may simu-late an exodeviation and produce pseudostrabis-mus. An existing exodeviation will look worsethan it actually is, or it may mask all or part of anesodeviation.

If the fovea’s position is nasal to the point atwhich the optical axis cuts the globe’s posterior

FIGURE 12–3. Angle kappa. A, When the ob-server places his or her eye in line with thelight located on the subject’s line of sight, thereflection of that light appears displaced na-salward on the cornea. B, When the examinerbrings his or her eye and the light into line withthe patient’s pupillary axis, the reflection of thelight appears centered.

FIGURE 12–4. Definition of angles. C, center of rotation;F, fovea; N, nodal point; O, point of fixation; P, center ofpupil; X, point of cornea that lies in the central pupillaryline; AB, optical axis; AP, central pupillary line; OC, fixationaxis; OF, visual axis; angle ONA, angle alpha; angle OCA,angle gamma; angle OPA, angle kappa; angle OXA, anglekappa, as measured clinically. Angle lambda not defined.(From Lyle TK, Wybar KC: Lyle and Jackson’s PracticalOrthoptics in the Treatment of Squint [and Other Anoma-lies of Binocular Vision], ed 5. Springfield, IL, Charles CThomas, 1967.)

pole, the corneal reflection of a light fixated bythat eye will appear to lie on the temporal side ofthe pupillary center. In this case the term negativeangle kappa is used. A negative angle kappa maysimulate an esodeviation and again produce apseudostrabismus, may make an existing esotropialook worse than it actually is, or may mask all orpart of an exodeviation. Pseudoesotropia second-


FIGURE 12–5. The angle kappa. The angle is called posi-tive when the light reflex is displaced nasalward andnegative when it is displaced templeward. (From Noor-den GK von: Atlas of Strabismus, ed 4. St Louis, Mosby–Year Book, 1983, p 33.)

ary to nasal displacement of the fovea may becaused by high myopia. A negative angle kappais less common than a positive angle kappa, but itis not correct to say that a negative angle kappais always pathologic.28; 104, p.290 This statement,which has been repeated in many texts, especiallyorthoptic texts, gives the wrong impression. Fun-dus examination does not always reveal visibleanomalies when a negative angle kappa is present.

FIGURE 12–6. Pseudostrabismus caused by ectopic macula. A, The patient appears to have a largeright exotropia (XT). The Hirschberg test showed an XT of 20� to 25�. B, No shift of OD occurs whenOS is covered. C, Fundus photographs reveal an ectopic macula. The tip of the fixation target (X)indicates the position of the fovea, which is displaced several disk diameters templeward. The retinalblood vessels are pulled over templeward. This patient had been born prematurely and for severalweeks was kept in an incubator with high oxygen concentration. (From Noorden GK von: Atlas ofStrabismus, ed 4. St Louis, Mosby–Year Book, 1983, p 35.)

However, because of traction of the retina incases of retinopathy of prematurity, a true patho-logic ectopia of the macula is accompanied by apositive angle kappa. The macula is pulled in thetemporal direction, causing pseudoexotropia (Fig.12–6). Other causes of ectopic macula includescarring from Toxocara canis retinitis or congeni-tal retinal folds. The condition may be bilateraland may occur in siblings.43

A vertical angle kappa, simulating a hyperdevi-ation, is usually (but not always11) caused by supe-rior or inferior displacement of the macula from aretinal scar.

Measurement of Angle Kappa

For clinical purposes it suffices to observe theposition of the corneal light reflection while thepatient fixates monocularly on a penlight. To avoidparallax, the examiner’s eye must be aligned withthe fixation light. A more accurate determinationof the angle formed between the visual and pupil-lary axes can be made by observing catoptric(Purkinje) images using, for example, Tscher-ning’s ophthalmophacometer,122 which consists ofa telescope on a graduated arc provided with suit-able lights. With the visual axis of the subjectcoincident with the axis of the telescope, the Pur-kinje images are displaced sideways or vertically,


depending on the orientation of the phacometer.Fixation on a small object moved along a gradua-ted arc brings the Purkinje images into the centerof the pupil, and the optical axis is now coincidentwith the telescope’s axis. The angle kappa is mea-sured by determining the distance in degrees bywhich the fixation object has to be moved alongthe arc. This elegant and accurate instrument is nolonger available and has been replaced by lessprecise but clinically useful methods.

Shifting of fixation and therefore of the visualline is used to measure the angle with a majoramblyoscope. A special slide, bearing a horizontalrow of letters and numbers separated by intervalsof 1� or 2�, is inserted into one arm of the majoramblyoscope. The patient is asked to fixate thezero, and the position of the corneal light reflec-tion is observed. The patient shifts fixation to eachof the letters or numbers in turn until the lightreflection is centered on the cornea, which givesthe angle kappa in degrees. The angle is positivefor the right eye if fixation has to be shifted to thenumbers (left), negative if it has to be shifted tothe letters (right), and vice versa for the left eye(Fig. 12–7).

The angle kappa also may be measured clini-cally using a procedure similar to Tscherning’slaboratory method. A seated patient’s head is ad-justed in front of a perimeter arc. One eye isoccluded, and with the other eye the patient fixatesthe central fixation mark on the arc. The examinercloses one of the patient’s eyes and places a smallpenlight or ophthalmoscope light firmly under thelower lid of the open eye. The patient first placeshis or her head and the light in line with the visualaxis and observes the reflection from the cornea.If this reflection is not centered, the patient’s headis moved with the light until centering is achieved.At this point the light coincides with the opticalaxis. If the patient has to move the light to theleft for the right eye (temporally in relation to thepatient) or to the right for the left eye, the angle

FIGURE 12–7. Amblyoscope slide for the measurement of angle kappa.

kappa is positive. In contrast, when using themajor amblyoscope test, which is based on a dif-ferent principle, the patient must turn the right eyeto the left to compensate for a positive angle.

Size of Angle Kappa

Donders35 found a positive angle kappa that variedfrom 3.5� to 6.0� with an average of 5.082� inemmetropic eyes and from 6.0� to 9.0� with anaverage of 7.55� in hypermetropic eyes. In myopiceyes the angle kappa was generally smaller, aver-aging around 2.0�, and may even be negative.33

Donders’s findings that emmetropes and hyperme-tropes tend to have a larger angle kappa thanmyopes was confirmed in a more recent study byGiovianni and coworkers49 (Table 12–1). Althoughmean values reported by these authors are smallerthan those of Donders, they are in line with anaverage angle kappa of 2.6� as measured by Fran-ceschetti and Burian46 in a random population of334 subjects.

Clinical Significance of Angle Kappa

Since it may simulate, conceal,* or exaggerate adeviation, the angle kappa must be considered toobtain the best estimate of the actual deviation inpatients in whom this determination is made bythe corneal reflection test. When the deviation hasbeen so determined because of low visual acuityin one eye, an operation to improve the patient’sappearance is usually indicated. In such cases it isbest to disregard the angle kappa and its measure-ments. Cosmetic operations are performed tomake the eyes appear straight, not for aligning the

*Prof. Schweigger of Berlin is reported to have said of theangle kappa (Wiesinger126), ille mihi praeter omnes angulosridet (this corner [angle] smiles at me beyond all others)(Horace, Odes II, vi, 13) because of its role in the improvedappearance of some patients after not fully successful opera-tions.


TABLE 12–1. Distribution of the Angle Kappa in 483 Subjects with Emmetropia, Hypermetropia,and Myopia

Emmetropia Hypermetropia MyopiaNo. (mean) (mean) (mean)

Positive 180 73.9% (2.8�) 85.0% (2.4�) 75.85% (1.9�)Negative 208 10.5% (1.4�) 3.8% (2.1�) 11.6% (2�)Null 95 15.6% 11.2% 12.6%

Modified from Giovianni FG, Siracusano B, Cusmano R: The angle kappa in ametropia. New Trends Ophthalmol 3:27, 1988.

visual axes properly to facilitate binocular vision.If one were to aim at aligning the visual axes in apatient with a large angle kappa to facilitate binoc-ular vision, the relative postoperative position ofthe eyes might be cosmetic overcorrection or un-dercorrection. No mother would appreciate an ex-otropic appearance of her previously esotropicdaughter, even if the ophthalmologist could assureher quite correctly that the visual axes are nowparallel.

Observation of Head Position

Patients with comitant heterotropias, especiallythose with comitant horizontal heterotropias, usu-ally carry their head in a normal position, butthere are exceptions.

In patients with nystagmus, the frequency andamplitude of the nystagmus may be reduced orthere may be no nystagmus when the eyes aredirected to one or the other side (see Chapter 23).In this position visual acuity is optimal. The pa-tient keeps the head turned to one side (e.g., tothe left) to bring the eyes into this optimal position(say, dextroversion) when looking straight-ahead.Patients who have a high amblyopia of one eyeoccasionally tend to turn their head in a directionaway from the amblyopic eye, especially whenreading or looking intently at an object. Patientswith infantile esotropia, manifest-latent nystag-mus, and strong fixation preference for one eyeoften have their face turn toward the side of thefixating eye (see Chapter 16).

Abnormal head positions in connection withincomitant and paretic deviations are usually as-sumed in the interest of obtaining binocular coop-eration or avoiding diplopia. Abnormal head posi-tions take either the form of tipping the chin upor down, a head turn (i.e., a turn around a verticalaxis), or a head tilt to one shoulder. For example,a patient with an A or V pattern of deviation (see

Chapter 19) may tend to carry the head with thechin depressed or elevated. On the other hand, apatient with a right lateral rectus paresis may turnthe head to the right, causing levoversion to bringthe eyes into a position in which the right lateralrectus muscle receives no impulses to contract.With these positions of head and eyes, patientsavoid diplopia and gain binocularity.

Bielschowsky wrote that ‘‘the patient choosesthe least inconvenient position of the head by whichthe paretic muscle is sufficiently relieved so thatbinocular single vision can be obtained.’’13, p.99 Inmany instances a patient will turn or tilt the headin the direction of the field of action of the pareticmuscle. However, if fusion cannot be attained witha compensatory head posture, the head may bepositioned to produce maximal separation of thedouble images. These and other aspects of com-pensatory head posture are discussed further inChapter 20. While an anomalous head postureshould alert the examiner to search for nystagmus;a paralytic horizontal, vertical, or cycloverticalstrabismus; cyclotropia; or an A or V pattern,normalcy of the head position does not rule outany of these conditions. Moreover, an ophthalmol-ogist must be aware that there are ocular causesunrelated to strabismus for an anomalous headposture, such as an uncorrected refractive error oranomalous retinal correspondence with a verticalangle of anomaly.24 Nonocular causes include fi-brosis of the sternocleidomastoid muscle, unilat-eral hearing loss, or psychogenic torticollis.

Several instruments have been developed toquantify the inclination of the head in degrees.104,

114, 115, 128 Among these a cervical range of motion(CROM) device used in physical medicine27 andin assessing craniomandibular disorders15 alsomeasures the degree of head turn and chin eleva-tion and depression. Such instruments are useful indocumenting and quantitating the effect of varioussurgical procedures on an abnormal head position.


Kushner70 has modified the CROM to assess limi-tations of ductions and the range of single binocu-lar vision at near and distance fixation.*

Determination of Presence ofa Deviation—Cover andCover-Uncover Tests

Inspection alone clearly is not always sufficient todetermine a manifest misalignment of the visualaxes. An epicanthus, facial asymmetry, or a wideangle kappa may simulate or conceal a deviation.The simple cover and cover-uncover tests estab-lish whether orthotropia or an ocular deviation ispresent, whether a deviation is latent or manifest,the direction of a deviation, the fixation behavior,and even whether visual acuity is significantlydecreased in one eye.

A cover is placed briefly before the eye thatappears to fixate while the patient looks at a smallobject, a figure pasted on a tongue depressor, or a6/9 visual acuity symbol. The test should alwaysbe done for distance and near fixation to establishany differences between the two conditions. As acover, one may use the palm of the hand or someform of occluder or paddle. Covering one eye ofa patient with normal binocular vision interruptsfusion.

If the patient has a heterotropia and the fixatingeye is covered, the opposite eye, provided it isable to do so, will make a movement from theheterotropic position to take up fixation, and thecovered eye will make a corresponding movementin accordance with Hering’s law. An exotropia ispresent when the eye taking up fixation movestoward the nose, an esotropia when it moves to-ward the temple, and so forth. If there is nomovement of the fellow eye, that eye is thencovered and the other eye is observed (Fig. 12–8).

When it has been established that no manifeststrabismus is present (no movement of the felloweye when either eye is covered), a cover-uncovertest will determine whether the patient has a latentdeviation (Fig. 12–9). Again, one and then theother eye is covered while the patient maintainsfixation. However, the examiner now directs atten-tion to the covered eye just as the cover is re-

*Performance Attainment Associates, 3550 LaBore Rd., Ste 8,St. Paul, MN 55110-5126; or Binoculus 740 Piney AcresCircle, PO Box 3727, Dillon, CO 80435-8727. Phone or faxUSA 970-262-0753, email: [email protected], website:BinocularVision.com

FIGURE 12–8. The cover test. A, Position of patient’seyes before the test. B, Cover placed over OS from theleft does not elicit a fixation movement of OD: no devia-tion of OD is present. C, Cover placed over OD from theright does not elicit a fixation movement of OS: no devia-tion of OS is present. D, OD moves outward to fixatewhen OS is covered: esotropia. E, OD moves inwardto fixate when OS is covered: exotropia. F, OD movesdownward when OS is covered: right hypertropia. G, ODmoves upward when OS is covered: right hypotropia.(From Noorden GK von: Atlas of Strabismus, ed 4. StLouis, Mosby–Year Book, 1983, p 39.)

moved. If the patient has a heterophoria, the cov-ered eye will deviate in the direction of theheterophoric position. When the eye is uncovered,it will move in the opposite direction to reestablishbinocular fixation, that is, toward the nose in exo-phoria, downward in hypertropia, and so forth.

Once the diagnosis of manifest strabismus hasbeen made, it is possible to establish the degree


FIGURE 12–9. The cover-uncover test. A,Cover has been removed from OD, and nomovement of OD can be detected: no latentdeviation of OD. B, Cover has been removedfrom OS, and no movement of OS can bedetected: no latent deviation of OS. If condi-tions A and B are present, the patient has nophorias that can be detected with this test.C, When uncovered, OS moves outward tofixate: esophoria. D, When uncovered, OSmoves inward to fixate: exophoria. E, Whenuncovered, OS moves down to fixate: lefthyperphoria. F, When uncovered, OS movesup to fixate: left hypophoria. The cover-un-cover test must be performed on both eyes.(From Noorden GK von: Atlas of Strabismus,ed 4. St Louis, Mosby–Year Book, 1983, p43.)

of alternation with the cover-uncover test. Thefixation behavior may vary from extreme monocu-larity, as in patients with deep amblyopia or strongocular dominance, to free random alternation. Inthe case of strong dominance the just-uncoveredeye will immediately resume fixation as the felloweye returns to its deviated position. In the case offree alternation the formerly deviated eye willcontinue to fixate after removal of the cover. Ifthe usually deviated eye continues fixation forsome time, for instance, until the lids close duringa blink, weak but definitive alternation is present.

The possible results of the cover and cover-uncover tests may be summarized as follows:

1. On covering the seemingly fixating eye:a. No movement of the other eye: there

was binocular fixation before applyingthe cover.

b. Movement of redress of the other eye:a manifest deviation was present beforeapplying the cover.

2. On uncovering the eye:a. Movement of redress of the uncovered

eye (fusional movement); no movementof the other eye: heterophoria is present.

b. No movement of either eye; uncoveredeye deviated; opposite eye continues tofixate: an alternating heterotropia is pres-ent.

c. Uncovered eye makes movement of re-dress and assumes fixation; opposite eyedeviates; preference for fixation with oneeye: a unilateral heterotropia is present.

The cover test also allows one to establish byobservation whether a gross eccentric fixation (seeChapter 14) is present in a patient with hetero-tropia. When the fixating eye is covered in suchusually esotropic patients, the deviated eye willmake no movement of redress or only a small,incomplete one.

Infants often object to having their heads or


faces touched. In such instances the examiner mayplace a paddle at some distance in the path of oneeye while holding a light or some other fixationobject with the other hand. This test, which hasbeen termed the indirect cover test, does not per-mit full interruption of fusion but is useful ininfants and small children with heterotropia (Fig.12–10).

When the cover test is applied to the fixatingeye in a strabismic infant and the patient consis-tently pushes the cover aside or performs search-ing, nystagmoid movements with the fellow eye,chances are high that visual acuity of that eyeis low and amblyopia must be suspected. Thisapplication of the cover test is of inestimablevalue in the diagnosis of amblyopia in infants (seeChapter 14). A pseudoptosis (see Fig. 12–1), ifpresent, will disappear when the fellow eye iscovered. The cover test may not reveal ultrasmalldeviations as seen in microtropia (see Chapter 16),but in most patients this limitation does not reducethe value of this simple test.

A clinically useful modification of the covertest was introduced by Spielmann112 after havingbeen mentioned briefly by Javal.66 Instead of anopaque cover a translucent occluder is usedthrough which the examiner can observe or evenphotograph the covered eye, but through whichthe patient sees only diffuse light without con-tours. By using the Spielmann occluder the diag-nosis of heterophoria is simplified because thedeviation of the covered eye can be directly ob-served by the examiner without having to removethe cover (see Fig. 8–1). Covering both eyes withtranslucent occluders permits a quick preliminary

FIGURE 12–10. The indirect covertest. The occluder is placed betweenthe patient’s eye and the fixation ob-ject. (From Noorden GK von: Atlas ofStrabismus, ed 4. St Louis, Mosby–Year Book, 1983, p 41.)

determination of whether an esotropia is of refrac-tive-accommodative or nonaccommodative origin(Fig. 12–11). In the first case the eyes willstraighten after covering both eyes; in the secondthe esotropia will persist. Further applications ofthe cover test with translucent occluders are dis-cussed in Chapters 18 and 23.

Measurement of Deviation

Tests used to diagnose strabismus usually are clas-sified as objective and subjective. Objective testsas performed in clinical practice, and even certainlaboratory tests, reduce cooperation of the patientto the ability to hold steady fixation. The ophthal-mologist performs certain manipulations, makesobservations, and draws conclusions from theseobservations. When using subjective tests the oph-thalmologist also performs certain manipulations,but the patient’s response determines the results;that is, the patient must make observations andreport them.

The opinion is widespread that objective testsare more reliable and therefore preferable to sub-jective tests.17 Objective is equated with ‘‘good,’’subjective with ‘‘bad.’’ This is erroneous. In com-mon usage objectivity in making a judgment hascome to mean that the judgment is not tainted byone’s prejudices and feelings. However, in subjec-tive tests for measuring the state of the sensoryand motor visual system, a patient’s feelings, prej-udices, and sense of value are no more suspectthan the feelings, prejudices, or value judgmentsof the examiner. Also, the premise that the patient


FIGURE 12–11. A patient with refractive-accommodativeesotropia may have A, manifest esotropia withoutglasses; B, orthotropia when the stimulus to accommo-date excessively is suspended with translucent occludersof Spielmann112; and C, orthotropia with glasses.

is a less keen or more biased observer than theophthalmologist is by no means necessarily cor-rect.

The truth is that most subjective tests are inher-ently more precise than objective tests. The enor-mous precision of the great body of psychophysi-cal investigations of the visual system, which areall based on subjective testing, is the best evidencefor the value of these tests. Many diagnostic andtherapeutic decisions in ophthalmology are basedon an assessment of visual acuity, which dependsentirely on a patient’s response. Is this responseless reliable or trustworthy than, say, the patient’slocalization of double images on any of the diplo-pia tests? The sensory system can be evaluatedclinically only by subjective responses of the pa-tient, although there are laboratory methods thatpermit the sensory system to be assessed objec-tively.

When using subjective tests, one expects a pa-tient to be able and willing to cooperate. Verbalresponses to a change in a stimulus situation can-not be expected of an infant or someone who isseverely mentally defective nor can objective testsrequiring attentive fixation be performed on suchpatients. All tests have their limitations; not alltests are suitable for every age level and everyperson. This does not make one test intrinsicallybetter or worse than another. The art of the oph-thalmologist consists of judiciously applying testsin each case that provide the maximum amount ofcorrect information needed for appropriate treat-ment.

Prism and Cover Test

The prism and cover test, or the alternate covertest, is deservedly popular. It is also known as the

screen cover test, but this term is misleading andshould be avoided.72

To perform this test, a cover is placed alter-nately in front of each eye while the patient main-tains fixation. The eye that is uncovered makes amovement of redress in the direction opposite thatof the deviation. The amount of the deviation isgrossly estimated, and a prism of a strength lessthan the estimated deviation is placed in the appro-priate direction in front of one eye. To measureesotropia, the prism must be placed base-out, foran exotropia base-in, for a right hypertropia base-down in front of the right eye or base-up in frontof the left eye, and for a left hypertropia base-down in front of the left eye or base-up in frontof the right eye. This manipulation reduces themovement of redress, and the prism strength isincreased until the movement is offset (Fig. 12–12).

Combinations of horizontal and vertical devia-tions are frequent. In such patients it is best to firstneutralize the horizontal deviation with prisms andthen to add prisms to stop the vertical deviation.At that point, it may be necessary to further cor-rect the horizontal deviation. The amount of prismstrength required to offset all movements of re-dress is a measure of the deviation. Cyclodevi-ations cannot be measured in this fashion, andmust be determined either subjectively or with themajor amblyoscope.

Physiologic Basis

Redress in the prism and cover test is a psycho-optical reflex movement that occurs when the eyefixates. The sensory origin of this reflex movementstems from stimulation of a peripheral retinal area


FIGURE 12–12. The prism and cover test. A, Right eso-tropia. B, When OS is covered, OD moves outward totake over fixation. C, When the cover is transferred toOD, OS moves out to take over fixation. D, A prism,base-out, is held before OD; the cover is transferred toOS. There is still outward movement of OD when takingover fixation, although the amplitude of this movementis decreased by the effect of the prism (compare withB). E, The cover is again transferred, and a prism ofgreater power is held before OD. F, Transfer of cover toOS does not elicit fixation movement of OD. The devia-tion is offset by the prism, and the power of this prismequals the deviation. (From Noorden GK von: Atlas ofStrabismus, ed 4. St Louis, Mosby–Year Book, 1983,p 49.)

in the deviated eye by the fixation object. Fixationcauses the eye to turn in such a way that thefixated object is imaged on the fovea. The move-ment is quantitative and is directly proportionalto the distance of the fovea from the stimulatedperipheral area. Placing prisms of increasingpower in front of the eyes brings the image of thefixated object closer and closer to the fovea, caus-ing a corresponding decrease in the movement ofredress. When the prism strength equals the

amount of deviation, the image falls on the fovea.There is no longer an incentive to move the eye,and the movement of redress ceases (Fig. 12–13).

Performance

As is true of most tests to diagnose strabismus,the prism and cover test is technically very simple,yet findings can be misleading unless the test isunderstood and performed correctly. To properlyperform this test, use adequate fixation objects anda technique that will ensure maximum dissociationof the eyes.

A penlight should never be used as a fixationobject. For distance fixation a 6/9 visual acuitysymbol is recommended or, in the case of a prelit-erate patient, electrically operated, moving me-chanical toys or projected moving cartoons. Fornear fixation, a similar visual acuity symbol orsome small picture or object can be used. Smallcutout figures pasted on the end of a tongue de-pressor are convenient for testing children, whoare asked to identify the object (Fig. 12–14).

To maintain the child’s interest, paste pictureson the ends of both sides of the tongue depressorand change the object if the child’s attentionwanes. The examiner should place him- or herselfat the desired distance, 33 cm, and then ask thechild to hold the tongue depressor against the endof the examiner’s nose. This serves two purposes:to keep the examiner’s hands free and to helpmaintain the child’s interest in fixating. Instead ofusing a tongue depressor, the examiner may clipa small card to the bridge of his or her glasses(Fig. 12–15).

The reason for using fixation objects ratherthan a simple penlight is to control accommoda-tion during measurement of the deviation at nearand distance fixation. One must understand that apatient’s response depends on the stimulus pre-sented, not only during subjective tests, where itis more obvious, but also during objective tests.

Another important consideration is the mannerin which the test is performed. Maximal dissocia-tion of the eyes must be achieved to make thecorrect diagnosis, especially in patients with heter-ophoria. Such patients have a strong compensatoryinnervation that keeps their eyes aligned and it isnot immediately suspended when one eye is cov-ered. It is necessary to dissociate the eyes forsome time to bring out the full amount of thedeviation. The test must not be performed hur-riedly, and the cover should be placed alternately


FIGURE 12–13. Optical principles of prism and cover test. A, Image of object fixated by OD isprojected on the nasal half of the retina of OS. B, When OD is covered, OS moves outward to takeover fixation. Under the cover, OD performs an inward movement of equal amplitude, followingHering’s law of equal innervation. C, When a prism of sufficient power offsets the nasal displacementof the image, OS will no longer change its position when OD is covered (compare with Fig. 12–12,F). (From Noorden GK von: Atlas of Strabismus, ed 4. St Louis, Mosby–Year Book, 1983, p 51.)

FIGURE 12–14. Tongue depressors provided with photographically reduced Snellen letters andpictures for use as fixation objects.

FIGURE 12–15. Photographically reduced Snel-len letters mounted on the frame of the examin-er’s glasses.


over each eye a few times. Most important, thepatient should never be permitted to regain fusionwhile the cover is being transferred. In patientswith an exodeviation, one eye may have to beoccluded for 30 to 45 minutes. The difference inmeasurements before and after occlusion may besignificant (see Chapter 17).

In contrast to this brief occlusion is the pro-longed occlusion test developed by Marlow80 inan attempt to uncover the full amount of hetero-phoria, particularly a hyperphoria. Marlow oc-cluded the nondominant eye for 14 days and noless than 7 days to accomplish thorough dissocia-tion of the eyes and was convinced of the effec-tiveness of this procedure in uncovering clinicallysignificant amounts of heterophoria. Prominentophthalmologists99 of Marlow’s time supported hisobservations which have been reconfirmed in arecent study, using more critical methods of inves-tigation.87 However, the clinical significance ofthese findings remains questionable. Duane andBerens37 stated that unilateral occlusion producesan artificial hyperphoria, an opinion shared byLancaster.73 It has yet to be shown that smalldegrees of horizontal and vertical heterophoriaunveiled only by prolonged unilateral occlusionhave any impact on the patient’s ability to fusewithout symptoms of asthenopia. Today, the testof Marlow has probably only historical interestand should not be confused, as it is frequently inthe German strabismus literature, with the occlu-sion test introduced by Scobee and Burian for thediagnosis of a pseudodivergence excess type ofexodeviation (see Chapter 17).

Another way to ensure full dissociation andobtain the full amount of the deviation is to addprism power not only until redress is stopped butalso until a reversal of the direction of movementis noted. In so doing, one frequently finds that theendpoint is higher than originally thought. Thistechnique is recommended for routine use.

To gain insight into a patient’s deviation, per-form the prism and cover test for distance and nearfixation with the patient first wearing refractivecorrection and then with the correction removed.Comparison of these four figures allows one todraw conclusions about the part played by accom-modation in the patient’s deviation. The deviationmeasured in distance fixation while the patient iswearing full correction excludes accommodation.The fusion factor must be excluded as far aspossible by a properly performed prism and covertest. With the influence of accommodation and

fusion controlled, one obtains the static or basicdeviation or static (basic) angle of squint. If cor-rection of the refractive error is inadequate, ac-commodation is uncontrolled and one then obtainsthe dynamic deviation or dynamic angle of squint.Likewise, in the case of insufficient dissociation ofthe eyes, persistent strong compensatory fusionalinnervation during the prism and cover test willcause dynamic factors to override and obscure thestatic deviation.

Precise definition of these terms is important toavoid misunderstanding. This has not always beenthe case in the European strabismologic literaturein which different meanings have been given toclassic terms in discussions of the nystagmusblockage syndrome.1, 31, 57, 86 For example, dynamicangle has been used synonymously with variableangle and it has been said that ‘‘the smallestobserved angle is always the static angle.’’ We,on the other hand, define a variable angle of stra-bismus as a deviation that increases or decreasessignificantly while the patient is being examinedor, when measured on different occasions, whiletesting conditions remain equal and accommoda-tion and fusion (dynamic factors) are fully con-trolled. A good example of a variable angle is thatwhich occurs in a patient with an acute nystagmusblockage syndrome who has a variable angle ofesotropia of a size that is inversely related to thenystagmus intensity (Chapter 23). It is also nottrue that the static angle is always smaller than thedynamic angle. For instance, fusional convergencemay cause a larger static deviation to decrease atnear fixation in patients with a simulated diver-gence excess type of exotropia (Chapter 22), or apatient with intermittent exotropia may use ac-commodative convergence to control the deviationat distance fixation (smaller dynamic angle). Con-trolling the accommodative state by asking thispatient to read the 6/6 line on the visual acuitychart at 6 m distance will unmask the larger staticdeviation. Also, if the angle of a comitant hori-zontal strabismus is greater in primary positionthan in extreme lateral gaze, dynamic factorsshould not be blamed for this difference. We be-lieve this phenomenon can be explained on simplemechanical grounds: the excursion of each eye inlateral positions of gaze is checked by orbitalstructures.32 Thus a fully adducted eye can nolonger exhibit excessive adduction in esotropes,and excessive abduction in exotropic patients canno longer be effective once an eye is fully ab-ducted. Consequently, depending on individual


variations of the effectiveness of these ‘‘brakes,’’the angle of strabismus in lateral gaze may besmaller than in primary position. This ratherlengthy explanation is necessary to define clearlythe terms dynamic, static, and variable angle asused throughout this text.

Another useful modification of the prism covertest is to repeat it while the patient is fixating at 33cm distance and looking through �3.00D lenses,clipped over the distance correction or, in the caseof emmetropia, placed in the trial frame. Withthe accommodative demand for near fixation thuseliminated, the deviation at near should now ap-proximately equal that at distance. Single clip-onlens holders are commercially available (Fig. 12–16).

It is recommended that the prism and covertest also be performed with either eye fixating. Todo this, one eye is made to fixate while the otheris alternately covered and uncovered and a prismis placed before the covered eye to stop movementof that eye. The process is then repeated with theother eye fixating. Differences in the amount ofprism power required for each eye indicated thepresence of a primary and secondary deviation(see Chapter 20) or an incomitance, for example,induced by an operation.

The prisms to be used in the test may beloose, in sets, or so-called prism bars or ladders,consisting of a row of prisms of increasing power.When using prism bars, two are necessary: one tomeasure the horizontal deviation and one to mea-

FIGURE 12–16. Halberg clip-on lens holder.

sure the vertical deviation. One also may use thehorizontal bars with loose prisms held vertically.

To establish the basic deviation, the eyes mustbe tested in the clinical primary position for bothdistance and near fixation with and withoutadditional plus lenses. Measuring the near devia-tion with the eyes in the reading position, asScobee106, p. 300 suggested, is not desirable, becausethe possible presence of a V pattern of fixationmay simulate an accommodative factor when noneexists (see Chapter 19).

Limitations

The prism and cover test presupposes accuratefixation and cannot be performed if the deviatingeye is blind or has grossly eccentric fixation. Ineccentric fixation, the test provides wrong mea-surements, as the movement of redress of thedeviated eye stops when the stimulus falls on theeccentric retinal area used for fixation and notwhen it reaches the fovea. Test accuracy is alsolimited by the optical qualities of the prisms.1, 89, 97

The stronger the prisms, the greater the errors; butfrom a practical standpoint, it is of little impor-tance whether a deviation measures 75�, 80�, or85�. When large deviations are present, an erroras high as 10� is of no consequence for decisionson the treatment of the patient.

When using loose prisms one should rememberthat significant errors are produced when a low-power prism is added to a high-power prism. Ac-cording to Thompson and Guyton118 the effectproduced by adding a 5� glass prism to a 40�

glass prism is not 45� but 59�. This error can beminimized by holding one prism before each eye.These authors also point out that the amount ofdeviation neutralized by an ophthalmic prism isvariable depending on how the prism is held. Forinstance, a 40� glass prism with a posterior faceheld in the frontal plane gives only 32� of effect.Glass prisms are calibrated for use in the Prenticeposition; that is, the posterior face of the prism isperpendicular to the line of sight of the deviatingeye. Plastic prisms, on the other hand, are cali-brated for use in the frontal plane position, that is,parallel to the infraorbital rim.

When measuring large angle horizontal devia-tion with a prism bar one must be aware of thefact that even slight oblique shifts of the bar caninduce a vertical displacement of the image,mimic a vertical deviation, and cause vertical di-plopia.


Thompson117 (see also Scattergood and cowork-ers103) also drew attention to the artifacts intro-duced by spectacles lenses in measurement ofstrabismic deviations. Plus lenses decrease andminus lenses increase the measured deviation.This effect becomes clinically significant with cor-rective lenses with powers of more than 5D (seealso Adelstein and Cuppers1).

Test accuracy is limited further by the mini-mum movement of redress that the examiner candetect with the naked eye. Some experienced oph-thalmologists have claimed they can detect shiftsas small as 1.0� or even 0.5�. Ludvigh77 showedthat with cooperative patients, experienced observ-ers, and optimal conditions of illumination, 2�

would seem to be the limiting amount of observ-ers, and optimal conditions of illumination, 2� ersthe much less ideal conditions under which thetest is generally performed, it is probably safer toset the limit at 3� to 4�. Much the same resultswere obtained by Romano and von Noorden.98 Insome instances, on assuming fixation, either eyeovershoots the mark and returns to fixate the ob-ject of attention with a secondary corrective eyemovement. For example, in esotropia the eyemakes a larger outward movement than one cor-responding to the angle of squint and then mustturn inward to assume fixation. In these cases theendpoint of the test is not exact, but an approxi-mate measurement can usually be obtained. Ac-cording to Mehdorn and Kommerell,81 this ‘‘re-bound saccade’’ may be caused by failure ofsuppression to be released instantly on coveringthe fixating eye. Certainly one can reasonablyassume that such a mechanism would decreaseprecision of a preprogrammed corrective eyemovement.

It is evident also that if nystagmus is present,an accurate determination of the deviation by theprism and cover test may be difficult if not impos-sible. The nystagmus need not be manifest butmay occur only when one eye is covered. This isthe so-called latent nystagmus, a rather rapid,jerky form with its quick phase toward the uncov-ered eye. More about this interesting form of nys-tagmus is found in Chapter 23.

Prism and Cover Test in DiagnosticPositions of Gaze

The prism and cover test is useful in determiningincomitance in otherwise comitant deviations,confirming by measurement the degree of a pare-

sis, and establishing what muscle or muscles areinvolved in a paralytic condition. To this end, thedeviation should be measured in the nine diagnos-tic positions of gaze. The first is the primaryposition; next come the secondary positions ofright, left, up, and down; and last the tertiarypositions of up and right, up and left, down andright, and down and left.

In the past, the eight secondary and tertiarypositions have been called cardinal positions andare so designated, even in some recent textbooks.In discussing the physiology of ocular motility,only the secondary positions, reached by thecardinal movements, are so termed. To preventconfusion it is better to use the term diagnosticpositions, since tertiary positions are included. Theterm has the added advantage of reminding theophthalmologist that these positions are primarilyfor establishing certain points in the diagnosis.The practical field of fixation in the unrestrictedcasual use of the eyes is rather narrow (p. 79).Results of tests made 25� or 30� from the primaryposition in any direction may not be meaningfulfor the patient’s use of the eyes, but they aremeaningful in making diagnostic points. Devia-tions present only in extreme positions may notrequire surgical treatment. To determine whethera deviation is paretic or paralytic, the relativeposition of the eyes in diagnostic positions shouldbe measured with either eye fixating, as has beendescribed for the primary position.

Various techniques have been proposed to diag-nose paretic involvement of a vertical muscle,58, 60,

96, 124 all of which include the head tilt test as afinal step. The head tilt test, the obliquity of hori-zontal or vertical double images (see Chapter 15),and similar tests actually are confirmatory ratherthan primary tests. They are not essential to thediagnosis, although they can be helpful in complexcases such as congenital paralyses with greater orlesser spread of comitance, marked overaction ofan antagonistic muscle, and preexisting horizontalor vertical heterophoria or heterotropia. For rela-tively recent and simple pareses or paralyses ofvertically acting muscles, however, answers to thefollowing three questions will definitely establishthe diagnosis: (1) Is there a right or left hyperdevi-ation in primary position? (2) Does the hyperdevi-ation increase in elevation or depression? (3) Doesthe hyperdeviation increase in dextroversion orlevoversion? These questions are answered by ex-amining the versions and by comparing the posi-tion of the eyes in the various directions of gaze


or, better yet, by measuring them with the prismand cover test. The answer to the first question isobtained from the cover test; the answer to thesecond informs one whether a right or left elevatoror depressor muscle is at fault; and the answer tothe third determines whether the vertical rectus orthe oblique muscle is involved. Thus the diagnosisis established. Further details about examinationof patients with cyclovertical deviations may befound later in this chapter and in Chapters 18and 20.

In practical performance of the prism and covertest in diagnostic positions of gaze, varying proce-dures are followed. Accommodative targets shouldbe used as fixation objects to minimize variabilityof the deviation resulting from variations in ac-commodation. Such a target may be handed to thepatient to hold and the hand placed successivelyin the desired positions, leaving the examiner’shands free to perform the test (Fig. 12–17). Forthe experienced ophthalmologist this method maybe fully satisfactory, but it does not permit accu-rate repetition of the test. So-called deviometerstherefore have been designed that permit all pa-tients being tested to bring the eyes as closely aspossible into the same positions. A perimeter arcon which an accommodative target could beplaced for measurement of the deviation in fixa-tion above and below the horizontal plane wasdescribed by von Noorden and Olson.88 Such aperimeter arc can be placed in the horizontal andtertiary positions and makes a good deviometer.

In the Motility Clinic of the Department ofOphthalmology at Baylor College of Medicine,Houston, Texas, a deviometer built from scrap

FIGURE 12–17. Example ofprism and cover measurementoutside primary position. Patientis looking up and to the left.

metal is used in which retroilluminated slidesstimulate accommodation. Each slide is positioned35� from the primary position119 (Fig. 12–18).

One great advantage of using a deviometer isthat the prism and cover test can be performedin diagnostic positions under exactly the sameconditions on different occasions and thus permitmeaningful comparison of test results (e.g., preop-erative and postoperative).

Measurement with the MajorAmblyoscope

The angle of deviation can be measured also byusing a major amblyoscope. These devices, pat-terned after the Hering haploscope (see p. 72), arebasic orthoptic instruments. They are especiallyuseful for studying the sensory state of the patientand in nonsurgical treatment.

The essential parts of major amblyoscopes (Fig.12–19) are a chinrest, a foreheadrest, and twotubes carrying targets seen through an angled eye-piece, one for each eye. The tubes are placedhorizontally and supported by a column aroundwhich they are movable in the horizontal plane. Amirror, one in each tube, reflects the image of thetarget through the eyepiece into the correspondingeye. The distance between the tubes can be ad-justed so that the centers of the eyepieces corre-spond accurately to the patient’s interpupillary dis-tance. When this is done and if the head and chinare properly adjusted, the axes around which thetubes turn should be in line with the center ofrotation of the eyes. In addition to adjustments forhorizontal positions of the arms, there are controls


FIGURE 12–18. The Boyse-Smith deviometer. (From Toosi SH, Noorden GK von: Effect of isolatedinferior oblique muscle myotomy in the management of superior oblique muscle palsy. Am JOphthalmol 88:602, 1979.)

that allow a vertical separation of the targets, aswell as cyclorotational adjustment. The amount ofall these displacements can be read from scales,which are usually graduated both in arc degreesand prism diopters. The tubes may be locked andmoved together horizontally and in some modernmodels also vertically. The illumination systemfor each target can be controlled individually toincrease or decrease the stimulus luminance to

FIGURE 12–19. A major amblyoscope. (Courtesy ofClement & Clark.)

one eye. Keys are provided to manually flash thelight, illuminating either target. The flashing alsocan be controlled automatically in certain models,with a wide range of light-dark intervals. Thisbasic instrument may be equipped with a greateror lesser number of refinements. Some models aredesigned to produce afterimages or Haidinger’sbrushes.

The main difference between laboratory haplo-scopes and major amblyoscopes is the way inwhich accommodation is controlled. The targetcarrier in the haploscope can be moved along thearm, which is graduated in diopters. The positionof the targets in the major amblyoscope is fixedin the focal plane of a �6.0D or �6.5D lens sothat they are at optical infinity, which should pre-vent accommodation from affecting the deviation.However, the fact that targets are actually a shortdistance from the eyes causes proximal conver-gence to enter into play. Consequently, the devia-tions measured with the major amblyoscope indistance setting are frequently larger than thoseobtained with the prism and cover test in distancefixation.8, 46, 117 One major British amblyoscope(the Curpax Major Synoptiscope No. 10) usessemitransparent mirrors in lieu of opaque mirrorsin front of the eyes, a feature already used in thehaploscope of Ames and Gliddon,2 which allowsthe patient to view a distant object on which thetarget images in the slide holders on each arm are


superimposed while deviation is being measured.In this way the influence of proximal convergenceis avoided.78, p. 105

To induce accommodation, auxiliary minuslenses are placed in front of the eyepieces. Formeasurements at near fixation (e.g., of thevergences), minus lenses are used in the amountrequired to offset the plus lenses in the eyepiecesand the arms are set at 18D (for the convergencerequirement of a 6.0 cm interpupillary distance),which thus becomes the zero setting for a 33 cmviewing distance.

The deviation is measured by moving the armsof the major amblyoscope into such a position thatimages of the target fall on the respective fovealareas. This is done by moving the arms until thereis no further refixation movement of the eyes inan alternate cover test (either by actual coveringor by alternately extinguishing the light on oneside of the instrument). Vertical displacements ofthe target carriers measure vertical components ofthe deviation. Finally, it is also possible to rotatethe targets around an anteroposterior axis and thusevaluate and measure cyclodeviations.

Conventional amblyoscopes do not permit de-termination of the angle of strabismus in periph-eral positions of gaze whereby the eyes are disso-ciated by the patient’s nose or orbital margins. Yetsuch measurements are important, especially inthose patients with paretic or paralytic strabismus.These difficulties have been overcome by theSynoptometer (Oculus) of Cuppers, which is amodified amblyoscope that permits measurementof deviations by means of mirrors in peripheralpositions of gaze of up to 50� in dextroversionand levoversion, 50� in elevation, and 60� in de-pression.31, 85

To avoid the distraction of infants and childrenthat is caused by instrumentation or by prismsand occluders switched directly before the eyes,Guyton developed an ingeniously designed remotehaploscope to be used in combination with aninfrared television-based eye tracker.54, 56 The ef-ficiency of measurement of an ocular deviationwith this apparatus in terms of speed and repeat-ability is superior to conventional methods.Campos and colleagues25 developed a similar sys-tem in association with a computerized deviometerwhich allows one to follow automatically step-by-step the various diagnostic procedures in comitantand paralytic strabismus. There are many potentialresearch applications for such systems, but it isquestionable whether this technological extrava-

gance will eventually replace the older tests in aclinical environment.

Corneal Reflection Tests

If the deviated eye is blind or has low visualacuity or, in young children, is unable to maintainfixation for longer than a moment, the amount ofthe deviation cannot be determined by the prismand cover test or by any subjective tests. Onemust then resort to estimation of the deviation byobserving the first Purkinje image using the so-called corneal reflection test. The corneal reflec-tion is on the nasal side of the deviated eye inexotropia, on the temporal side in esotropia, belowthe corneal center in hypertropia, and above it inhypotropia.

Hirschberg63 first suggested the use of cornealreflection for measuring ocular deviations, andhis test is still widely used. Based on a simplecalculation, Hirschberg found that each 1 mm ofdecentration of the corneal reflection correspondedto 7� of deviation of the visual axis (Fig. 12–20).His assistant, du Bois-Reymond,38 determinedwith a modified arc perimeter that if the cornealreflection in the deviated eye is found to be in thepupil, the deviation ranges from 0� to 20�, givena pupillary diameter of 3.5 mm. If it is on the irisbetween the pupillary margin and the limbus, anangle of 20� to 45� may be present. If the reflec-tion appears on the conjunctiva, a deviation of 45�or more exists.38

Brodie16 reexamined the conversion factor

FIGURE 12–20. The Hirschberg test. For explanation,see text. ET, esotropia. (From Noorden GK von: Atlas ofStrabismus, ed 4. St Louis, Mosby–Year Book, 1983,p 45.)


given by Hirschberg over 100 years ago and pho-tographed the corneal reflection of normal subjectswho were fixating visual targets separated by 10�

over a range of 200�. A value of 12� per millime-ter displacement of the reflection was determinedin Brodie’s study, which is similar to numbersreported by subsequent investigators.34, 44, 93, 102 Thediscrepancy between the traditional (7�/mm) andthis new factor may be caused by the fact that aphotograph records the true reflex displacement inthe frontal plane, which differs from a measure-ment of the reflex displacement from the cornealapex along the corneal surface.16 The rather widerange of measurements reported by different au-thors (10.7� to 15.6�) could be explained by thefact that the reference landmarks (corneal center,pupillary center, limbus) and the calibrationmethod were not the same in all studies.

Paliaga and coworkers92–94 have revived themethod of objective strabismometry, which wasquite popular about a century ago. With a millime-ter ruler, they measured displacement of the cor-neal light reflection that occurs in the deviated eyeas this eye assumes fixation. The linear displace-ment of the reflection is then converted into angu-lar values (see also p. 200).

Another method is based on the well-estab-lished principle of Hering’s law of equal innerva-tion to the two eyes. Corneal reflection is pro-duced in the two eyes by an appropriately placedpenlight, which is fixated by the patient’s bettereye. The examiner places him- or herself on theside of the deviated eye to avoid parallax errorsin observation (Fig. 12–21).

Prisms are then placed in front of the fixatingeye to center the corneal reflection in the deviatedeye. The amount of prism power necessary toachieve this is a measure of the deviation. Thistest, first described by Krimsky,69 who suggestedthe name ‘‘prism reflex test,’’ is a practical methodof estimating the size of the angle of squint inpatients with a blind or deeply amblyopic eye withor without eccentric fixation. It is important forthe examiner to be seated directly in front of thedeviating eye to avoid false readings caused byparallax. In another version of this test, prisms areplaced in front of the deviating eye until the cor-neal reflection is centered. However, observationof the corneal reflection through prisms is difficult,which is why we prefer the procedure outlined.

Strabismometric methods based on the corneallight reflection remain rather crude and are not asprecise as the prism and cover test because the

FIGURE 12–21. The Krimsky test. A–C, Prisms, base-out, of increasing power are placed before the fixatingeye until the light reflex is centered on the cornea of thedeviating eye. D, Optical principles of the prism reflextest. (From Noorden GK von: Atlas of Strabismus, ed 4.St Louis, Mosby–Year Book, 1983, p 47.)

deviation at distance fixation is difficult to mea-sure with this method, accommodation cannot becontrolled while maintaining fixation on a pen-light, the angle kappa is included in the measure-ment, and, as shown by Choi and Kushner,29 inter-pretation of the position of the light reflection onthe cornea differs widely even among experiencedobservers. Be this as it may, the Hirschberg andKrimsky tests are valuable methods to obtain anapproximate measurement of the angle of strabis-mus in patients too young to cooperate with theprism and cover test or when poor visual acuityin one or both eyes precludes adequate fixation.

Photographic Methods

Barry and coworkers9 developed a method to mea-sure the angle of strabismus in infants and children


photographically (see also Lang75). The apparatusconsists of a camera with three horizontallyaligned flashes and a small fixation light. Theangle of strabismus is derived from the reflectionpattern in the pupil of the first and fourth Purkinjeimages from each light source. The accuracy issaid to be between 2.0� and 4.5�, which wouldmake it superior to the Hirschberg test. Friedmanand Preston47 use a two-flash Polaroid camera toscreen for amblyopiogenic factors, such as strabis-mus, media opacities, and refractive errors. Photo-graphic methods for visual screening of childrenlack accuracy because accommodation is not con-trolled by an appropriate fixation target. Evalua-tions of the efficacy of this method to detectamblyopiogenic factors have thus far yielded con-troversial results. One study concluded that thephotoscreener holds promise as a useful massscreening tool,91 but others have shown that thephotographs may be noninterpretable or thatamblyopiogenic factors were missed in 20% ofchildren evaluated with this method.105, 110 Photo-screening is probably more accurate than screen-ing for these factors by the pediatrician,120, 125 butcannot and should not take the place of a completeophthalmologic examination.

Bruckner Test

Bruckner18 introduced a test to diagnose strabis-mus in infants that is based on judgment of theposition of the corneal light reflex and the colorof the light reflected from the fundus. A brightcoaxial light source emitted by a direct ophthal-moscope illuminates both eyes of the patient si-multaneously from a distance of 1 m in a semi-darkened room. The position of the cornealreflection and differences in the brightness of thefundus reflex between the two eyes are noted bythe observer through the ophthalmoscope. In thepresence of strabismus the reflex of the fixatingeye is darker than in the deviated eye, a phenome-non that had been previously noted by Worth.127

It has been estimated that this technique can beautomated to detect the presence of 2� to 3� ofocular misalignment based on the difference inbrightness of the bright pupil images between thetwo eyes.84 In a second step one eye is illuminatedat a time, and the pupil size, its reaction to light,and fixation movements are noted to detect ambly-opia. Whether this test is a reliable screeningmethod for strabismus is another matter since ithas been reported that asymmetrical fundus re-

flexes occurring in infants up to 10 months of agemay represent a normal stage of development4 andthat the tests yield false positives in nonstrabismicsubjects.52

Subjective Tests

Subjective tests for estimating the deviation of thevisual axes have a long and honorable history. Allthe great names, and many of the near-great ones,in Germany, England, and the United States havemade their contribution to this chapter of the in-vestigation of neuromuscular anomalies of theeyes. The story has been fascinatingly retold bySloane,111 but in this book the discussion must berestricted to tests in current use.

If the two visual axes are not properly aligned,the patient should have diplopia. The diplopia iseither spontaneous, as in recent extraocular muscleparalyses or acute comitant strabismus, or it mustbe elicited artificially if suppression or anomalouscorrespondence (see Chapter 13) is operative incasual seeing, as is the rule in comitant squint. Ifcorrespondence is normal, the distance of the dou-ble images may be used as a measure of deviation.

All subjective tests for measurement of thedeviation are based either on the diplopia princi-ple or the haploscopic principle.

Diplopia Tests (Red-Glass Test andOthers)

In the diplopia type of test (Fig. 12–22), onedetermines the subjective localization of a singleobject point imaged on the fovea of the fixatingeye and an extrafoveal retinal area in the othereye. In esotropia, where the image of the fixationpoint in the deviated eye falls on a retinal areanasal to the fovea, there should be uncrossed dip-lopia. In exotropia, where the image of the fixationpoint in the deviated eye falls on a retinal areatemporal to the fovea, there should be crosseddiplopia. If retinal correspondence is normal, dou-ble images not only should be properly orientedbut also should have a distance equal to the angleof squint. The distance of the double images isthen a measure of the deviation; but even withspontaneous diplopia it is difficult if not impossi-ble for the patient to state whether the images arecrossed or uncrossed. The two visual fields mustbe differentiated and for this purpose a red glassis placed in front of one eye (hence, red-glasstest; see Fig. 12–22). The patient fixates a smalllight source and states whether the red light is to


FIGURE 12–22. Principle of diplopia tests. (FromBurian HM: Normal and anomalous correspon-dence. In Allen JH, ed: Strabismus OphthalmicSymposium, II. St Louis, Mosby–Year Book,1958, p 184.)

the right or to the left and above or below thewhite light. If the white fixation light is in thecenter of a Maddox cross (Fig. 12–23), the patientmust state the numbers near which the red light isseen. If the patient is seated at the correct distance,these numbers indicate the amount of deviation.

The red glass not only must differentiate thetwo fields but also must dissociate them, which isespecially important in patients with heterophoria,intermittent heterotropia, and particularly with in-termittent exotropia. In these patients, one wantsto ascertain the full amount of the deviation. Forproper dissociation of the fields, the red glass mustbe dark enough to make it impossible for thepatient to see anything but the red fixation lightto prevent fusional impulses from the surround-ings of the fixation light.

The test is facilitated if it is begun by alter-nately covering the eyes of the patient to showthat a white light is seen with one eye and only asomewhat dim red light with the other eye. Whenboth eyes are uncovered, the patient is more likelyto become aware of the double image of the light.Nevertheless, eliciting diplopia in patients withcomitant heterotropia is often difficult, but withpatience and skill it can invariably be achieved.One must occasionally have recourse to the simpletrick of placing in front of the eye a 10� or 15�

prism base-up or base-down together with the redfilter. As a rule, this throws the image outside thesuppression scotoma and the patient immediatelyrecognizes diplopia. Vertical displacement of theretinal image introduced by the prism must betaken into account when this maneuver is used.

In general, in doing the red-glass test, the filtershould be placed before the fixating eye, which isless likely to suppress the darkened image of thefixation light, but one should always attempt torepeat the test by placing the red filter in front ofthe other eye. For various reasons, responses arenot always identical. In patients with a paralyticcondition, a primary and secondary deviation maybe present (see Chapter 20). Retinal correspon-dence may change with a change in fixation (seeChapter 13). Frequently a dissociated vertical de-viation may occur. If the deviation is large, it issometimes necessary to reduce it with prisms; butit is not advisable to fully correct the angle, sincethis may lead to the phenomenon of horror fu-sionis (see p. 136). However, in some instancesthe ophthalmologist may want to investigate theresponse of the two foveas to simultaneous stimu-lation (e.g., before suggesting an operation). Forthis purpose the deviation must be fully neutral-ized with prisms.

The red-glass test used in conjunction with aMaddox cross can be performed successfully incooperative children as young as 4 years of age.Such children should not be asked to tell wherethey saw the light, but they should be asked to goto the scale and put their finger on the place wherethey saw it. It is then wise to place a verticalprism first base-up and then repeat the test base-down. This makes it easier for the child to locatethe position of the double image and serves as acheck on the reliability of the report. Alternateuse of vertical prisms is recommended in all casesin which the patient’s answer is doubtful.


FIGURE 12–23. The Maddox cross. A, The test is performed at 5 m but can also be performed at 1m, in which case the small numbers on the Maddox cross (not shown in this figure) indicate theangle of separation of the two images. This patient has a right esotropia of 4�. B, If both foveashave a common visual direction (normal retinal correspondence) the red light will appear in the samevisual direction as the number whose image is formed on the fovea of the deviating eye. In thiscase the light appears on the number 4. C, Homonymous diplopia in an esotropic (or esophoric)patient with a deviation of 4�. (From Noorden GK von: Atlas of Strabismus, ed 4. St Louis, Mosby–YearBook, 1983, p 61.)

To determine the presence and amount of in-comitant deviations with the red-glass test, onemay chart the so-called diplopia fields. This testis best done by turning the patient’s head so as tobring the eyes into the various secondary andtertiary diagnostic positions, ascertaining in eachposition the distances of the double images andmarking them on an appropriate chart. For grossorientation in near fixation a quick and helpfulprocedure is to keep the patient’s head straightand to move a penlight up, down, right, left, andso on and to ask the patient whether the distance

of the double images is greater in gaze up, down,right, or left. The test can be made quantitativeby using a device suggested by Sloane,111 whichconsists of a small, hand-held, transparent screenprovided with a tangent scale designed for a view-ing distance of 0.5 m and having a small fixationlight in its center. The patient uses a pointer toindicate the position of the double image. To testin secondary and tertiary positions, it is necessarythat the patient’s head be turned. Figure 12–24shows a diplopia field in a patient with a recentparesis of the left superior rectus muscle. Vertical


FIGURE 12–24. Diplopia field in a patient with a recent onset of a left superior rectus paresis.Vertical diplopia is present only in left upper gaze because of underaction of the paretic muscle andsecondary overaction of the right inferior oblique.

diplopia is present only when the patient looks upand to the left where underaction of the left supe-rior and secondary overaction of the right inferioroblique muscle are present.

A special tangent scale devised by Harms,59

further developed by Mackensen,79 and widelyused mainly in Germany has a fixation light in itscenter, covered by a metal box. When this box isremoved, in lieu of the round fixation light, ahorizontal streak of light may be used to determinethe obliquity of double images by placing a redglass in front of the observer’s eye. The amountof obliquity may be read from a scale. When thetangent scale is used with a fixation light, thepatient also wears a red glass in front of one eyeand indicates the position of the red light bymeans of a green ring projected by a small projec-tion device handled by the patient. In addition tothe usual markings, an oblique cross at 45� on thetangent scale makes it possible to test the verticaldeviations with the patient’s head tilted to the rightand left shoulders. Proper position of the patient’shead is monitored with a special projector attachedto the forehead.

A handy, routinely used method of measuringthe amount of heterophoria is to replace the redglass with a white or preferably red Maddox rod.

This device, consisting of small glass rods, causesan astigmatic elongation of the fixation light andmay be placed to produce a vertical or horizontalstreak to measure the horizontal and vertical devi-ation. If the streak does not go through the fixationlight, prisms of increasing strength are placed infront of the eye until it does. The amount of prismpower required to achieve this goal is a measureof the heterophoria (Figs. 12–25 and 12–26). Theamount of the heterophoria in near fixation alsomay be measured with the Maddox wing test,78, p. 200

the heterophorometer,13, p. 41 or similar devices, allbased on the diplopia principle. As has beenpointed out, all tests require that the retinal corre-spondence be normal. Their application to thestudy of retinal correspondence is discussed inChapter 13.

Haploscopic Tests

Haploscopic tests differ from diplopia tests in theirmode of stimulation. Two test objects rather thanone are presented to the patient, who is requiredto place them in such a fashion that they appearsuperimposed (Fig. 12–27). Again assuming thatcorrespondence is normal, the two objects areplaced to stimulate the foveae of the two eyes.


FIGURE 12–25. A, Maddox rod in testing position forhorizontal heterophoria. B, Patient sees the line goingthrough the light: no horizontal phoria is present. C, Theline is seen to the left of the light (crossed diplopia):exophoria. Add prisms, base-in, to OD until the line iscentered on the light. The power of the prism is read andequals the amount of phoria. D, The line is seen to theright of the light (uncrossed diplopia): esophoria. Addprisms, base-out, to OD until the line is centered. (FromNoorden GK von: Atlas of Strabismus, ed 4. St Louis,Mosby–Year Book, 1983, p 53.)

The visual fields of the two eyes are differenti-ated and dissociated in various ways. Each eyemay be presented with a different target, as isdone when using a major amblyoscope. Also,complementary colors may be placed in the visualfield of the patient, either directly or by projection,and each eye may be provided with a correspond-ing colored filter. Instead of color differentiation,a Polaroid projection system or some other sys-tem, such as the phase difference projection haplo-scope of Aulhorn5 (see p. 74), may be used.

Color differentiation is convenient in clinicalpractice. It is applied, for instance, in the Lancas-ter71, p. 78 red-green test (Fig. 12–28), which uses awindow shade type of screen that can be rolledup when not in use. The screen is ruled intosquares of 7 cm so that at a distance of 2 m eachsquare subtends approximately 2�. The squares are

all of the same size and the tangential error is nottaken into account. Lancaster claimed that at 2 mdistance this error did not produce a significantinaccuracy. The patient is equipped with red-greenreversible goggles. Two projectors are used: agreen projector, handled by the patient, and a redprojector, handled by the examiner. The imageformed by the projector is linear. The red filtermay be placed in front of either eye to investigatedifferences caused by changes in fixation. Insteadof inverting the glasses, the examiner can ex-change projectors with the patient. The examinerprojects the line from his or her projector onto thescreen at any desired place, the patient’s head isheld steady, and the patient is asked to place thestreak from his or her projector so that it appearsto the patient to coincide exactly with the otherstreak. If one assumes that correspondence is nor-mal, the two streaks will be separated objectivelyon the screen by an amount corresponding to thedeviation of the visual axes. The positions of thestreak shown by the patient are entered into asmall chart on which the screen is reproduced.

FIGURE 12–26. A, Maddox rod in testing position forvertical phoria. B, No vertical phoria is present. C, Righthypophoria (usually left hyperphoria also). Add prisms,base-down, to OS until the line is centered. D, Righthyperphoria. Add prisms, base-up, to OS until the line iscentered. (From Noorden GK von: Atlas of Strabismus,ed 4. St Louis, Mosby–Year Book, 1983, p 53.)


FIGURE 12–27. Principle of haploscopic tests.(From Burian HM: Normal and anomalous cor-respondence. In Allen JH, ed: Strabismus Oph-thalmic Symposium, II. St Louis, Mosby–YearBook, 1958, p 184.)

Since the projected image is a line, the patient’sresponse may indicate the presence of cyclotropiawhen the streak is tilted. The Lancaster red-greentest is most useful in patients with ocular paraly-sis. It is least useful in patients with heterophoriasor intermittent heterotropias since suppression isnot perfect. Reducing the ambient illuminationlessens the unwanted effect of fusional stimuli.

The same holds true when the eyes are dissoci-ated with Polaroid material.19 When such tests areused, the position of the patient’s head must befixed and maintained in a headrest. Even slighttipping of the head will reduce the angle betweenthe analyzer in front of the patient’s eyes and thepolarizer in front of the projectors and reduce theextinction.

The Hess screen test 62 (Fig. 12–29) is based onthe haploscopic principle. It was popularized byLyle, in particular for diagnosing possible pareticor paralytic conditions in patients with normalcorrespondence. To perform this test, a black cloth3 ft wide by 31⁄2 ft long, marked out by a seriesof red lines subtending between them an angle of5�, is used. At the zero point of this coordinatesystem and at each of the points of intersection ofthe 15� and 30� lines with one another and withcorresponding vertical and horizontal lines, thereis a red dot. These dots form an inner square of 8dots and an outer square of 16 dots. An indicatoris provided consisting of three short green cordsknotted to form the letter Y. The end of the verticalgreen cord is fastened to a movable black rod 50cm long. The ends of the other two cords are kept

taut by black threads that pass through loops tosmall weights at corresponding upper corners ofthe screen. This arrangement enables the patientto move the indicator freely and smoothly overthe whole surface of the screen in all directions.The patient wears red-green goggles and is seated50 cm from the screen, preferably with his or herhead fixed in a headrest. The patient now sees thered dots with one eye and the green cords withthe other and is instructed to place the knot joiningthe three green cords over each of the red dots inturn. The examiner marks the positions indicatedby the patient on the small card with a reducedcopy of the screen. The points found by the patientare connected by straight lines and permit theexaminer to determine which, if any, muscles reactabnormally. To change fixation, the red-green gog-gles are reversed with the red filter now in frontof the left eye.

Measurements of the angle of strabismus thatare based on image separation with red and greenglasses or other haploscopic methods have becomejustifiably popular in many countries, especiallyin Europe. Provided the patient is cooperative,these tests are precise and repeatable on differentoccasions. However, they are less popular in theUnited States, partially because they are somewhattime-consuming and require a prolonged attentionspan and reliable patient responses, which ex-cludes a large segment of pediatric patients withstrabismus problems.

Subjective determinations of the angle of devi-ations with the major amblyoscope, also based on


FIGURE 12–28. Lancaster red-green test. A, Equipment for the test. B, Charts to record results.(Courtesy of Luneau and Couffignon, Chartres, France.)


FIGURE 12–29. The Hess screen test. A, The screen. B, Chart for recording the results (From LyleTK, Wybar KC: Lyle and Jackson’s Practical Orthoptics in the Treatment of Squint [and OtherAnomalies of Binocular Vision], ed. 5. Springfield, IL, Charles C Thomas, 1967.)

the haploscopic principle, are aimed primarily atestablishing the sensory state of the patient andare discussed in Chapter 13.

Measurement of Cyclodeviations

Qualitative Diagnosis Based onPosition of Double Images

The measurement of cyclodeviations in clinicalpractice relies largely on subjective tests. In pa-tients who have spontaneous diplopia or who canbe made to appreciate diplopia by interruptingfusion with alternate covering of the eyes, cyclo-deviations can be grossly estimated by holding aruler horizontally with the straight edge in frontof their eyes and slightly below the midline. Ifone of the cyclovertical rotators is involved, therewill be vertical diplopia. By alternately coveringthe eyes, the examiner then ascertains to whicheye the higher or lower image belongs and askswhether the two rulers seen by the patient appearcloser on the right or on the left. To avoid anymisunderstanding, one should draw a horizontalline and then let the patient add the obliquely seenline. For quantitative determination of cyclotropiathe Lancaster red-green test may be used.

The tilt of the retinal image is opposite the tiltof the horizontal line, as seen by the observer.Therefore, when the line is seen slanted towardthe nose (to the left for the right eye or to theright for the left eye), an excyclodeviation is pres-ent. Tilting of the line down toward the templewill indicate the presence of an incyclodeviation.For correct interpretation refer to the diagramshown in Figure 12–30. A simple mnemonic ruleis that the line is always tilted in the direction inwhich the offending muscle would rotate the eyeif it were acting alone. Since, for example, thesuperior oblique is an intortor in addition to beinga depressor, paralysis of that muscle will causethe image seen by the involved eye to appearlower and slanted toward the nose.

Maddox Double Rod Test

For quantitative determination of a cyclodeviation,red and white Maddox rods are placed in a trialframe, the red before the right eye and the whitebefore the left eye (Fig. 12–31). The direction ofthe glass rods is aligned with the 90� marks of thetrial frame. A small scratch on the metal frame ofthe Maddox rods facilitates this alignment. Specialcare must be taken to avoid tilting the trial frames


FIGURE 12–30. Subjective appearance and retinal image of a horizontal line seen by the left eye. A,In the absence of a cyclodeviation. B, With incyclotropia. C, With excyclotropia. V and H, The verticaland horizontal meridians of the retina; UT, UN, LT, and LN, the upper and lower temporal and nasalquadrants of the retina; VI, the resulting visual impression.

during the test. The patient looks through theMaddox rods and is shown a penlight, the imagesof which appear as horizontal streaks. A verticalprism may be added to separate the images foreasier identification. If one of the lines (say, thered one) appears slanted toward the nose (Fig.12–31A), excyclotropia of the right eye is present.The red Maddox rod is then turned by the ophthal-mologist (or by the patient) until the red line isseen parallel with the white line (Fig. 12–31B). Ifat the end of this adjustment the scratched markpoints, for example, toward the 100� mark of theright trial frame, the patient has a right excyclo-tropia of 10�. In the presence of bilateral cyclo-tropia, for instance, excyclotropia of the right andleft eye in bilateral traumatic superior obliqueparalysis, both the red and white lines will be seenslanted toward the nose. The settings are repeatedtwo or three times. With good observers the mea-surements are extremely accurate. To test thecyclodeviation outside the primary position, shiftthe penlight to the right, left, above, and below,and repeat the test.

The Maddox double rod test is valuable as aqualitative test to substantiate a patient’s com-plaint about image tilting and to quantitativelydetermine the degree of tilt. However, the dissoci-ating characteristics of the test preclude cyclofu-sion, which is a most effective compensatingmechanism in cyclodeviations.100, 101 Thus theMaddox double rod test may indicate a cyclotropia

that, in some patients, may be clinically insignifi-cant under casual viewing conditions that permitcyclofusion. Moreover, since ocular dominancedetermines the patient’s response to the Maddoxdouble rod test, contradictory results with respectto the laterality of the paralyzed muscle are com-mon.90

Simons and coworkers109 have shown that thetwo-color format of the Maddox double rod test,with the red rods placed before the right eye andthe clear rods before the left eye, may produceartifactual localization of the image perceivedthrough the red rods in patients with superioroblique paralysis. Thirty-three of 40 patients(83%) localized the excyclodeviation to the eyeviewing through the red Maddox rods, regardlessof the laterality of the paralysis or the fixationpreference. To avoid this artifact and the influenceof peripheral visual clues the authors suggestedthat red Maddox rods be placed before both eyesand that the test be performed in a dark room. Todistinguish which eye is cyclodeviated one Mad-dox rod is then slightly rotated back and forth inthe trial frame and the patient is asked whether itis the horizontal or tilted luminous line that is‘‘rocking.’’

Bagolini Striated Glasses

To test for cyclotropia under casual viewing condi-tions, we replace the Maddox rods with the stri-


FIGURE 12–31. The Maddox dou-ble-rod test. For explanation, seetext. (From Noorden GK von: Atlasof Strabismus, ed 4. St Louis,Mosby–Year Book, 1983, p 57.)

ated glasses of Bagolini.7 Like Maddox rods, theseglasses produce an image of a streak of light,perpendicular to the axis of the striations whenviewing a punctate light source, without, however,obstructing surrounding fusible visual details. Theglasses are placed in the trial frame with the axesof striation pointing toward the 90� mark. If thepatient is unable to fuse the two vertical lines, theglasses are turned until fusion occurs and theamount and direction of the cyclotropia is read offthe trial frames as during the Maddox double rodtest.100 The use of the Bagolini glasses to test forretinal correspondence is discussed in Chapter 14.

Major AmblyoscopeTo test for cyclotropia, the targets positioned inthe arms of this instrument are rotated around an

axis until there is no more movement of redressof the eye that takes up fixation. The amount ofcyclodeviation, expressed in degrees, can be readoff the instrument.

Ophthalmoscopy and FundusPhotographyIndirect ophthalmoscopy and fundus photographyare useful auxiliary methods to diagnose cyclo-tropia. As early as 1855 and not long after theinvention of the ophthalmoscope by von Helm-holtz (1851), von Graefe51 pointed out an apparentvertical displacement of the optic disk in cyclo-deviations and discussed using ophthalmoscopy tostudy the action of muscles involved in cyclo-rotations of the globe. Normally, the average loca-tion of the fovea in relation to the optic nerve


head is 0.3 disk diameter below a horizontal lineextending through the geometric center of the op-tic disk. From this position, an imaginary hori-zontal line will cross the optic nerve head justbelow the halfway point between its geometriccenter and lower pole (Fig. 12–32A). The rangeof variation of this relationship in nonstrabismicpersons is indicated by the solid lines in Figure12–32A. Incyclotropia is present when the foveaappears above a line extending horizontally fromthe center of the optic nerve head (Fig. 12–32B),and excyclotropia is present when the fovea isbelow a line extending horizontally from just be-low the lower pole of the optic disk (Fig. 12–32C).The fovea’s position may vary slightly betweenthe two eyes, but a difference of 0.25 or more ofa disk diameter in the vertical position should beconsidered abnormal.14

To measure the amount of torsion accuratelywhile viewing the fundus through a 60D lens on

FIGURE 12–32. A, Average foveal position (dashed line) and range of normal (solid line). B, Fundusin patient with incyclotropia. C, Fundus in excyclotropia. (From Bixenmann WW, Noorden GK von:Apparent foveal displacement in normal subjects and in cyclotropia. Ophthalmologica 89:58, 1982.)

the slit lamp, Spierer113 suggested projecting ahorizontal slit beam on the retina so that it crossesthe fovea while the patient fixates on a targetstraight-ahead with the other eye. In the presenceof cyclotropia the examiner tilts the slit beam untilit crosses the fovea on one side and the borderbetween the center and lower third of the opticdisk on the other side. The amount of tiltingneeded for this position to occur is then read offthe scale mark on the slit lamp. De Ancos andKlainguti3 described a special lens to measure theangular displacement of the lower border of theoptic disk with respect to the fovea during indirectophthalmoscopy.

Discrepancies between sensory and motor as-pects of cyclodeviations, as expressed in differ-ences between subjective (Maddox double rodtest, Bagolini lenses) and objective (ophthalmos-copy, fundus photography) findings, are discussedin Chapter 18.


The ‘‘New Cyclo Test’’

The New Cyclo Test,* introduced by Awaya andcoworkers,6 is similar in principle to the Awayatest for aniseikonia (see p. 121) and based onhaploscopic image separation with red-green spec-tacles. A red half-moon is viewed through thegreen glass and a green half-moon through the redglass. In a series of printed figures the green half-moon is tilted in a stepwise fashion. The patientselects the figure in which the two half-moonsappear to be aligned and the amount of cyclodevi-ation in degrees is then read off this figure.

Scotometry

Locke76 showed that the vertical displacement ofthe blind spot in cyclotropic eyes may be used todetermine its degree. This method, while precise,is rarely used in clinical practice.

Determination of the SubjectiveHorizontal or Vertical

Determination of the subjective horizontal or ver-tical with and without spatial clues distinguishesbetween the contribution of such clues to the adap-tation to cyclotropia. This method, almost forgot-ten now but once used widely in clinical practiceas part of the workup of a patient with paralysisof the cyclovertical muscles,61, 121 is still a usefuldiagnostic tool99 (see Chapter 18). The patientwhose head is stabilized views with either eye aluminous line that is projected in random obliquepositions onto an optically empty screen. The pa-

*Distributor for the Western Hemisphere: Binoculus (see p.174 for address).

FIGURE 12–33. The effect of occlusion in a patientwith dissociated vertical deviation. A, Orthotropia inprimary position. B, Elevation of the right eye andC, of the left eye when fusion is suspended withthe translucent occluder of Spielmann. (From Spiel-mann A: A translucent occluder for study of eyeposition under unilateral or bilateral cover test. AmOrthoptics J 36:65, 1986.)

tient then rotates the slide containing the line untilit appears exactly horizontal to him or her. Thedeviation from the objective horizontal as deter-mined with a carpenter’s level is measured by theexaminer with a protractor and indicates the de-gree of cyclotropia.

Measurement of DissociatedVertical Deviations

Bielschowsky12 classified vertical deviation intofour groups: (1) true comitant hyperphorias andhypertropias, (2) dissociated vertical divergence(alternating sursumduction), (3) paretic verticaldeviations, and (4) vertical deviations in the rightand left half of the field of fixation caused byprimary overaction of an inferior oblique muscle.The diagnostic differentiation of these forms isdiscussed in Chapter 18, but a few words must besaid about the diagnosis of dissociated verticaldeviation, commonly abbreviated as DVD.

In patients with DVD, the alternate cover testreveals that each eye turns upward under cover incontrast to the situation in vertical heterophoria.After removal of the cover, the eye makes a slowdownward movement to reach the midline, attimes even going below it, accompanied by in-cycloduction. The translucent occluder of Spiel-mann112 is especially useful in the diagnosis of thiscondition and in demonstrating it to the patient’sparents (Fig. 12–33). As pointed out in Chapter18 a precise measurement of the vertical excur-sions of each eye during DVD is nearly impossiblebecause of the variable nature of this condition.

The Head Tilt Test

The maneuver of comparing the angle of strabis-mus with the head tilted successively toward one


and then the other shoulder, introduced by Hof-mann and Bielschowsky64 in 1900 and widelydeveloped by Bielschowsky, is known as the headtilt test. This useful test gives positive findingsregardless of whether the patient has any binocu-larity. The physiologic principles of the head tilttest and its application during the diagnosis ofcyclovertical deviations are discussed in Chapter20. The deviation may differ in various head posi-tions in patients with congenital and acquired pa-ralyses of the cyclovertical muscles when otherdiagnostic signs have become blurred with thepassage of time. Two valuable assets of the testare that the difference in the deviation can be seenand measured by the examiner and that it can bereadily used in examining young children whocannot yet respond to subjective tests. In someinstances it is difficult to see the difference in thevertical deviation in the head tilt test. In suchinstances a prism and cover test with the headtilted first to one shoulder and then to the other isadvisable. The prism should always be tilted sothat it has the same relation to the eye as inprimary position (Fig. 12–34).

Examination of the MotorCooperation of the Eyes

Ductions and Versions

Determination of the deviation amount in the ninediagnostic positions of gaze by means of the prism

FIGURE 12–34. Head tilt test with prism and cover mea-surement. Note that the prism is held so that its baseand axis are parallel with the palpebral fissure and notwith the floor.

and cover test or by one of the subjective testsestablishes certain important points in the diagno-sis. These points must be amplified by a study ofthe extent to which the eyes, singly or together,perform movements in various directions of gaze.

When examining ductions, cover one eye andhave the patient follow a penlight or other fixationtarget, bringing the eye to the farthest possibleposition in the directions right, left, up, down, upand right, up and left, down and right, and downand left. The examiner observes whether move-ment lags or is excessive in any direction.Bielschowsky13 pointed out that a study of theversions is of more value than a study of theductions. He stated that it is easier for the patientto overcome a weakness in the action of a muscleby a very strong innervational impulse during duc-tions than while performing version movements.

To study the versions, one places a penlight inthe midline before the patient’s eyes and moves itin the various directions, keeping the penlight atsuch a distance that one can always observe thecorneal reflections in both eyes. While doing so,carefully watch for excessive or defective move-ments in any direction. Remove the patient’sglasses to observe the movement of the eyes inperipheral positions of gaze.

In judging the normalcy of adduction and ab-duction, a gross but useful guideline is followed.In maximal adduction an imaginary vertical linethrough the lower lacrimal punctum should coin-cide with a boundary line between the inner thirdand the outer two thirds of the cornea (Fig. 12–35A). If more of the cornea is hidden, the adduc-tion is excessive (Fig. 12–35B). If more of thecornea is visible on maximal adduction and ifsome of the sclera remains visible, adduction isdefective (Fig. 12–35C ). If abduction is normal,the corneal limbus should touch the outer canthus(Fig. 12–35D). If the limbus passes that point andsome of the cornea is hidden, the abduction isexcessive (Fig. 12–35E ). If some of the scleraremains visible, abduction is defective (Fig. 12–35F ).

Guibor53, p. 28 rated overaction in adduction andunderaction in abduction on a scale of 1 to 4;however, he assigned no specific figures to thegrades of overaction or underaction. Urist123 devel-oped what he called the lateral version light reflextest, which is performed by holding a penlightexactly in the midline of the patient’s head at adistance of about 25 cm. The patient makes ex-treme dextroversions and levoversions. Normally,


FIGURE 12–35. The ductions of the eyes. A, Normaladduction. B, Excessive adduction. C, Defective adduc-tion. D, Normal abduction. E, Excessive abduction. F,Defective abduction. P, Lacrimal punctum. While the ver-sions are being tested, the fellow eye is kept open and,as a rule, fixates. The left eye is not shown in this figure.

the light reflex in the adducted eye should be onthe cornea at 35� temporally (Hirschberg scale)and at 10 mm nasally from the limbus on thesclera of the abducted eye.

A much more precise procedure is the limbustest of motility of Kestenbaum,68 intended espe-cially for evaluating the action of paretic muscles.This test avoids some pitfalls inherent to oldertests in attempting to determine the shift in relativeposition of certain fixed points in different posi-tions of gaze. The test is performed by holding atransparent millimeter ruler horizontally in frontof the cornea. In measuring abduction, the locationof the nasal limbus point is noted on the ruler inprimary position and in maximum abduction. Thedifference immediately gives the degree of abduc-tion in millimeters. Adduction is measured simi-larly by determining the positions of the temporallimbus. To measure elevation and depression, holdthe ruler vertically. The examiner should test eacheye with his or her own homonymous eye. Normalvalues established by Kestenbaum are 10 mm foradduction, abduction, and depression, and 5 to 7mm for elevation (Fig. 12–36). It is interesting tonote that there is no shift of the midpoint of theexcursions toward the nose in normal subjects.68

Patients with esotropia (infantile or accommo-dative; see Chapter 16) and alternating fixation orwith manifest-latent nystagmus (see Chapter 23)

may employ the left eye for viewing objects inthe right field of vision and the right eye forobjects in the left field of vision. No effort ismade to abduct the nonfixating eye, which showsan apparent limitation of abduction (Fig. 12–37Aand B). This behavior is called crossed fixationand in the older literature is also referred to astripartite fixation. To distinguish between pseudo-paralysis and true paralysis of the lateral rectusmuscle, the ductions of each eye are examinedwhile the fellow eye is patched (Fig. 12–37C ).

In general, the agreement between the measure-ments in the diagnostic positions and the behaviorof the versions is good, but there are exceptions.For example, simultaneous weakness of adductionin one eye and an excess of abduction in the othereye may offset each other and the abnormalitiesof the versions may not be apparent from thedifferences in measurements of the deviation.21

In watching pursuit movements of the eyes,one may find that the fixating eye will follow thelight, but the deviated eye will remain stationaryfor some time and then make a sudden movementin the direction taken by the fixating eye. Infre-quently, version movements (e.g., a dextroversionmovement) are replaced by vergence move-ments.22, 23

As a rule, children with comitant strabismuswill follow an appropriate fixation object withoutdifficulty. However, they frequently have muchmore difficulty in making version movements in adirection opposite that of the deviation (e.g., inlevoversion in a left esotropia). This behavior ismentioned briefly in the discussion of the etiologyof heterotropia.

Tests that distinguish between innervationaland mechanical-restrictive limitations of ocular ro-

FIGURE 12–36. The limbus test of Kestenbaum. (FromKestenbaum. A: Clinical Methods of Neuro-Ophthalmo-logic Examination, ed 2. New York, Grune & Stratton,1961, p 237.)


FIGURE 12–37. Crossed fixation. A, Children with esotropia may employ the left eye for viewingobjects in the right field of vision and B, the right eye to view an object in the left field of vision.Thus no effort is made to abduct the nonfixating eye, and the examiner must differentiate betweena true and a simulated abducens paralysis. C, Momentary occlusion of the fixating eye may notsuffice to force the fellow eye to take up fixation. D, Occlusion for several minutes may be requiredto restore good abduction. (From Noorden GK von: Atlas of Strabismus, ed 4. St Louis, Mosby–YearBook, 1983, p 121.)

tations (forced duction test, estimation of gener-ated muscle force, saccadic velocities) are dis-cussed in Chapter 20.

Elevation or Depression of theAdducted Eye (Upshoot orDownshoot in Adduction)When studying the versions, one often finds theadducted eye to be elevated. The phenomenonmay be unilateral or bilateral. This elevation inadduction is called strabismus sursoadductoriusand in the more recent American literature is alsoreferred to as upshoot in adduction. It is oftenoverlooked but important to note that overactionof the inferior oblique muscle is but one of several

causes for this phenomenon. Other causes are pa-ralysis of the contralateral superior rectus muscle,dissociated vertical deviation, certain forms ofDuane retraction syndrome, excyclotropia of theinvolved eye, and atopic muscle pulleys. The dif-ferential diagnosis of these conditions from pri-mary and secondary overaction of the inferioroblique muscle is discussed in Chapter 18.

Depression of the adducted eye, also calledstrabismus deorsoadductorius or downshoot in ad-duction, is seen with overaction of the superioroblique muscles, paralysis of the contralateral in-ferior rectus muscle (see Chapter 18), atopic mus-cle pulleys, and may also occur with Duane retrac-tion syndrome (see Chapter 21).


Measurement of Vergences

Determination of the vergences is of major impor-tance in examination of the motor state of a pa-tient’s eyes. It provides information about the pa-tient’s ability to cope with a deviation and isalso helpful in establishing the type of deviationaccording to Duane’s classification.36 The charac-teristics of the disjunctive ocular movements, thefusional movements or vergences, are discussedin some detail in Chapter 4. What follows dealswith their practical determination rather than thephysiologic basis of the tests.

To produce a vergence movement, retinal im-ages must be shifted so that they fall outside thePanum area of the retinal region under investiga-tion. Since the extent of that area in the fovealregion is roughly of the magnitude of 6 minutesof arc and since vergences are usually measuredwith bifoveal fixation, a shift of 1� is ample toproduce an image displacement capable of elic-iting a fusional movement.

Measurement With Prisms

The patient is seated comfortably and asked tofixate the appropriate object. A rotary prism isthen placed in front of one eye and moved toproduce the desired fusional movement. The prismmay be hand-held, or it may be part of a phoro-meter or phoropter. The prism strength is in-creased slowly and stepwise, and the patient isasked to report when the fixation object appearsdouble. When the patient reports diplopia, atwhich point the two images are rather suddenlyquite far apart, the required amount of prismpower is noted. It represents the limit of the pa-tient’s fusional amplitude in the direction tested,the so-called breakpoint. The prism power is thenreduced, again slowly and stepwise, and the pointat which the patient regains single vision is noted.This is the so-called recovery point.

Many ophthalmologists disregard the recoverypoint, depriving themselves of an important bit ofinformation. The recovery point indicates a pa-tient’s readiness to fuse the images. It should be2� to 4� below the breakpoint. If the breakpointfor convergence at near is, say, at 24�, the recoverypoint should be 20� to 22�. Some patients maynot recover until the prism power is much reduced,to 10�, 8�, or even 0�. This is especially commonin patients with intermittent deviations and indi-cates that once fusion is broken they have greatdifficulty regaining it.

When the convergence amplitudes are mea-sured, the patient will see singly and clearly up toa point. Beyond this point the fixation object willappear blurred but single until the breakpoint isreached, where the fixation point doubles up andagain is seen clearly. The point at which the blur-ring occurs is known as the blur point. It measuresthe limits within which accommodation can clearthe image of the fixation point in spite of increasedconvergence. The amount of fusional convergencethat can be elicited between the blur point andbreakpoint represents the absolute convergence.Orthoptists use accommodative targets to deter-mine the blur point and nonaccommodative targetsto determine the breakpoint.

Vergence movements are slow and tonic. Theymust be elicited by increasing the prisms slowlyto allow the patient to regain fusion after eachchange. If the prism power is changed too quickly,lower fusional amplitudes are obtained than ifthe test is properly performed. For a smooth andcontinuous increase of prismatic power we prefera rotary prism (Fig. 12–38) rather than a prismbar with a stepwise increase of prismatic power.One must also remember that when a strong im-pulse to perform a convergence movement hasbeen given, the tonic innervation does not sud-denly stop with removal of the stimulus but con-tinues for quite some time. If one starts by measur-ing the convergence amplitude and this is followedimmediately by measurement of the divergenceamplitude, divergence is opposed by the lingeringtonic innervation to converge. The resulting diver-gence amplitude is then likely to have a lowervalue than if it had been measured first becauseany fusion-induced vergence has an aftereffect41

that is stronger after sustained convergence thanafter divergence or vertical vergences. The longerthe duration of the vergence effort, the longer therate of recovery from the aftereffect.107 The bestmeans of reducing this effect is to induce a verti-cal vergence. The following order in testingfusional amplitudes is recommended: prisms base-out (convergence), prisms base-up (deorsumver-gence), prisms base-in (divergence), and prismsbase-down (sursumvergence).

Vergences should always be tested both in dis-tance and near fixation. Frequently they are testedat one fixation distance only (e.g., in distancefixation), especially when the divergence ampli-tudes are determined with a major amblyoscope.In patients who complain of difficulties in closework, especially when a convergence insufficiency


FIGURE 12–38. Objective measurement ofendpoint of vergence. A, Rotary prism atzero. The eyes are parallel. B, Rotary prismhas reached 26� base-out. The left eye is indivergent position.

is suspected, a comparison of the vergences indistance and near fixation is often very enlight-ening.

Since vergences are fusional movements, am-plitudes depend on the amount of fusible materialin the field of view of the person examined; thegreater the amount of fusible material, the largerthe amplitudes. They are smallest when a fixatinglight is seen in a completely dark room,50 and theycannot be elicited with dissimilar targets in a ma-jor amblyoscope. In 1948 Fink45 made a carefulstudy of this subject and recommended a 6/9 letteras a suitable fixation object. Actually, a smallfixation light serves the purpose well since itsdoubling up is most easily recognized by the pa-tient, provided the light is surrounded by amplefusible material (such as vertical and horizontallines) usually available in a well-lighted office.The images of this fusible material occupy thewhole of the two retinas and provide an adequatefusion stimulus.

Most patients are able to recognize diplopiawhen the breakpoint is reached, but some do notand instead suppress the image in the deviatedeye. Even in such instances the breakpoint can bedetermined by observation, at least in near fixa-tion. Both eyes will appear properly aligned aslong as they follow the vergence stimulus induced,

for example, by base-out prisms. As soon as thebreakpoint is reached, one eye will turn out (seeFig. 12–38).

The question most frequently asked and mostdifficult to answer concerns normal limits of thedifferent vergences. It is not possible to state inspecific numbers what the amounts of thevergences are or should be. Convergence normallyis larger than divergence, and vertical vergencesare smaller than either of the two. In some textsnormal limits for distance fixation are given as20� for convergence, 6� to 8� for divergence, and3� to 4� for sursumvergence and deorsumver-gence. Cyclovergence amplitudes may range be-tween 8� and 22�, depending on the size andorientation of the targets being used.30, 55, 67, 95

Horizontal vergences measured in distancefixation are smaller than those obtained in nearfixation, and the most useful data are probablystill those of Berens and coworkers10 (Table 12–2).These data were taken with prism bars in 104subjects with normal vision. Sharma and Abdul-Rahim108 reported larger vertical amplitudes (mean4.63�) than those found by Berens and coworkers.

Mellick82 used a variable prism stereoscope andthe synoptophore (a form of major amblyoscope)and two targets (a fusion target and a stereoscopictarget) to study horizontal fusional amplitudes in


TABLE 12–2. Average Vergence Amplitudes of 218 Men

Convergence Divergence Sursumvergence

At 6 m 14.1� 5.82� 2.54�

At 25 cm 38.02� 16.47� 2.57�

Data from Berens C, Losey CC, Hardy LH: Routine examination of the ocular muscles and non-operative treatment. Am J Ophthalmol10:910, 1927.

relation to age. He could find no significant influ-ence of age but did observe that the amplitude ofconvergence for distance and near vision wastwice as large when measured with the synopto-phore as when measured with a prism stereoscope.The average figures for his 561 subjects of allages are presented in Table 12–3. The data ofTait116 obtained from 500 ocularly normal subjects(Fig. 12–39) reflect the distribution of bothbreakpoint and recovery point.

From these figures it is evident that amplitudesof the vergences vary considerably from one per-son to another, even if function of the binocularsystem is normal. They are a measure in the motorsphere of a person’s responsiveness to disparatestimulation, as stereoscopic acuity is a measure ofa person’s responsiveness in the sensory sphere.

It is important to relate the vergence amplitudesto another individual characteristic, the hetero-phoric position for the distance at which the am-plitudes are measured. In this regard, measure-ments with a rotary prism may be misleadingunless they are properly understood. In performingthis test, the patient’s eyes start from the primaryposition, as defined clinically; that is, the eyesintersect in the fixation point, having already over-come any heterophoric position that might be pres-ent. The test with the rotary prism tells only howmuch additional vergence the patient can perform.Case 12–1 may make this point a little clearer.

TABLE 12–3. Mean Values and Standard Errors of Horizontal Vergences in 561 Subjects withNormal Neuromuscular Systems

Variable Prism Stereoscope Synoptophore

Fusion Target Stereoscopic Target Fusion Target Stereoscopic Target

Convergence amplitudesDistance 17.68 � 0.26 18.29 � 0.50 38.47 � 0.76 40.33 � 0.79Near 26.42 � 0.39 22.18 � 0.26 51.36 � 0.83 55.68 � 0.86

Divergence amplitudesDistance 7.97 � 0.10 9.00 � 0.15 10.78 � 0.12 11.77 � 0.16Near 13.61 � 0.16 12.04 � 0.15 12.63 � 0.13 13.36 � 0.16

Data from Mellick A: Convergence. An investigation into the normal standards of age groups. Br J Ophthalmol 33:725, 1949.

CASE 12–1

A 27-year-old woman had an intermittent exotropiafor distance of 22�, which she could control quitewell. Measured with rotary prisms for distance, shehad a convergence breakpoint at 8� and a diver-gence breakpoint at 26�. This appeared to be anobvious case of insufficient prism convergence andexcessive prism divergence, a conclusion that wouldonly be true if the zero position of the rotary prismhad a biological significance, which it did not. Actu-ally, this patient was able to overcome by conver-gence a divergent heterophoric position of 22� tokeep her eyes straight. With a rotary prism sheovercame an additional 8� of convergence. This pa-tient, then, in fact possessed a convergence ampli-tude of 30�, although her divergence beyond theheterophoric position was only 4�. The patient wasoperated on, and the deviation for distance wasreduced approximately to zero. Following the opera-tion, the amplitudes were found to be 30� of conver-gence and 6� of divergence.

Case 12–1 illustrates that measurements ofvergence amplitudes with a rotary prism are mean-ingful only insofar as they are related to the pa-tient’s heterophoric position, yet the absolute val-ues are not completely without significance. Theyindicate the reserve that the patient has beyondthe parallel position of the visual lines. A reserveof 8� of convergence, as the above patient had, isclearly insufficient. Such a patient may readily


FIGURE 12–39. Data of Tait forbreakpoint and recovery point in 500 sub-jects. A, Prism convergence. B, Prism di-vergence. (From Tait EF: Fusionalvergence. Am J Ophthalmol 32:1223,1949.)


experience diplopia under conditions of stress andannoying asthenopic symptoms.

In contrast, one may find remarkably large fu-sional amplitudes in patients with well-developedbinocular vision. This is particularly impressive invertical heterophorias in which fusional ampli-tudes may amount to 20� and more, especially incases of long-standing superior oblique muscleparalysis.

In 1900, Hofmann and Bielschowsky65 made athorough study of vertical fusional amplitudes andconcluded that they gradually increase by trainingup to a maximum value of 5.5� (approximately11�). Ellerbrock,40 on further investigation of verti-cal amplitudes, discovered that they were greaterin magnitude when larger fusional targets werepresented and when the rate of separation of thetargets was slower. He reported amplitudes aslarge as 7.5� to 8.4� (approximately 16�).42

An example of extraordinarily large verticalamplitudes, which developed in a patient whohad a hyperphoria throughout his life, is given inCase 12–2.83

CASE 12–2

A 42-year-old man who complained of blurring anddistortion at close work had been given glassesincorporating a correction for a mild hypermetropicastigmatism and 6� base-down for a correction of aright hypertropia (RHT). Our examination revealed avision of 6/4.5 in each eye with a correction of�1.00D sph �1.00D cyl ax 80� OD and �5.00Dsph �1.00D cyl ax 85� OS. With this correction hehad 10� of comitant RHT for distance and 12� ofcomitant RHT for near. He had excellent horizontalfusional amplitudes, and his vertical fusional ampli-tudes were extraordinarily large (24/16� of sursum-vergence and 24/10� of deorsumvergence). He hadsatisfactory binocular cooperation with a stereo-scopic threshold of 40 seconds of arc. The patientwas given his refractive correction with a readingadd but no prisms since he was so well adapted tohis motor anomaly. Over a follow-up period of 6years, his motor condition has not changed and hehas remained free of symptoms.

Measurement With a MajorAmblyoscope

When vergences are measured with a major am-blyoscope, the point of departure is the heteropho-ric position, that is, the arms are set at the patient’s

angle of deviation. From this position, variousvergence movements are induced by moving thearms (for the horizontal vergences) or the targets(for vertical and cyclovergences). This proceduredetermines total vergence amplitudes, but no in-formation is gained about the fusional reservebeyond the straight position of the eyes. This testcan be done also in heterophoric patients by start-ing with the arms of the major amblyoscope atzero. These measurements correspond to thoseobtained with the rotary prism.

Ordinarily, the major amblyoscope is adjustedfor optical infinity. Placing minus lenses of appro-priate strength in front of each eye and setting thearms at 18� adapt the instrument for near fixation,and vergences can also be measured for near vi-sual distance.

Targets that incorporate fusible material mustbe used to measure vergence amplitudes when amajor amblyoscope is used. Using targets thatcontain larger or smaller amounts of fusible mate-rial allows the effect of the amount of fusiblematerial on the amplitudes to be determined.

Fusional Movements Elicited byPeripheral Retinal Stimuli inStrabismus

Burian20 applied the peripheral fusion technique(see p. 74) in 75 patients with comitant strabismusand showed that patients with manifest strabismuscan display fusional movements. The main resultsobtained in eliciting fusional movements by pe-ripheral retinal stimuli can be summarized as fol-lows: patients with strabismus in whom peripheralfusional stimuli were effective, as a rule, experi-enced sensory disturbances (suppression, changesin mode of localization, changes in deviation)when the two retinal centers were stimulated si-multaneously; patients who did not follow periph-eral fusional stimuli did not have retinocentraldisturbances. Although the technique used in Buri-an’s studies is not directly applicable in ordinaryclinical practice to examination of patients, it canbe used to some extent in the major amblyoscopesby designing or selecting appropriate targets bothfor diagnostic and therapeutic purposes.

Near Point of Convergence

The near point of convergence (NPC) is deter-mined by placing a fixation object at 30 to 40 cmin the midplane of the patient’s head; the patient


FIGURE 12–40. Objective measurement of near point ofconvergence.

is then asked to maintain fixation on the object.The object is then moved toward the eyes untilone of the eyes loses fixation and turns out. Thedistance at which this occurs is the NPC. It ismeasured by a Prince ruler or similar device (Fig.12–40). This NPC lies approximately in the planeof the centers of rotation of the eyes.

The eye that maintains fixation at the NPC isgenerally considered to be the dominant eye, andthe deviated one is the nondominant eye. Determi-nation of the NPC is one of many tests suggestedfor establishing ocular dominance.

The NPC should be at 8 to 10 cm. A distancecloser than 5 cm is excessive. An NPC fartheraway than 10 cm is defective or remote. In pa-tients with convergence insufficiency, it may be asremote as 25 or 30 cm or more. As the test isrepeated, the NPC often comes closer to the eyes.The NPC is readily trained, except in extremecases of convergence insufficiency. On the otherhand, in a single testing session patients may makea special effort to converge and have a better NPCthan they actually use in casual seeing.

These statements are justified to some extentwhen the test is performed objectively. They alsoapply to the subjective form of the test in whichthe endpoint is established by the patient’s reportof diplopia. They very definitely do not apply tomodification of the subjective test as described byCapobianco26 and used routinely in our clinic. Inthis test a moderately dense red filter is placed infront of one of the patient’s eyes, preferably the

dominant eye. A penlight is held at a distance atwhich the patient can fuse the two images. Onepinkish light is then seen. The penlight is nowadvanced in the midline of the patient’s head, andthe point is noted at which binocular single visionis lost and diplopia is reported.

This test offers a slight obstacle to fusion, mini-mizes the effect of voluntary convergence, andyields results of diagnostic and prognostic value.In comparing findings in the objective test and thered-glass test, the following observations can bemade: (1) In patients with good convergence func-tion, results obtained with two tests are compara-ble and both are within normal limits; (2) in pa-tients with convergence insufficiency, thesubjective NPC is generally more remote than theobjective NPC and the difference may be quitelarge; (3) in patients with convergence insuffi-ciency who have a slightly remote NPC but inwhom the NPC established by the red-glass sub-jective test coincides with the objectively mea-sured NPC, the prognosis for speedy, successfulrecovery by treatment is good; (4) throughout thetreatment the NPC, as measured by the subjectivered-glass test, normalizes more rapidly than theobjectively determined NPC; and (5) at the suc-cessful completion of treatment, the NPC shouldnot only be normal but values obtained in theobjective and red-glass subjective tests should bein agreement.

Maintenance of Convergence

A patient not only must be able to converge theeyes to a near vision distance but also must beable to maintain convergence. This ability may betested by what is called, inaccurately, the dropconvergence test. When NPC is measured, an ob-ject is brought closer to the eyes. Accommodativeand fusional convergence are stimulated by theobject and assist in performance of the conver-gence movement. After bringing the fixation ob-ject into reading distance, ask the patient to main-tain convergence after the fixation object isremoved (‘‘dropped’’). Some patients are betterable than others to keep their eyes converged inthe absence of a fixation object.

REFERENCES

1. Adelstein FE, Cuppers C: Analysis of the motor situationin strabismus. In Arruga A, ed: International StrabismusSymposium (University of Giessen, 1966). New York, SKarger, 1968, pp 139–148.


2. Ames A Jr, Gliddon GH: Ocular measurements. TransSection Ophthalmol A M A 1928, p 102.

3. Ancos W de, Klainguti G: Mesure objective de la torsionoculaire: Une nouvelle loupe d’ophthalmoscopie indi-recte. Klin Monatsbl Augenheilkd 204:360, 1994.

4. Archer SM: Developmental aspects of the Bruckner test.Ophthalmology 95:1098, 1988.

5. Aulhorn E: Phasendifferenz-Haploskopie. Eine neueMethode zur Trennung der optischen Eindrucke beiderAugen. Klin Monatsbl Augenheilkd 148:540, 1966.

6. Awaya S, Miyuki I, Motoya M, et al: The New CycloTest and its clinical application. In Campos E, ed: Pro-ceedings of the Fifth Meeting of the International Strabis-mological Association (ISA). Modena, Italy, Athena Sci-entific Distributors, 1986, p 225.

7. Bagolini B: Tecnica par l’esame della visione binocularesenza introduzione di elimenti dissocianti: ‘‘Test del vetrostriato.’’ Boll Ocul 37:195, 1958.

8. Bagolini B: Ricerche sul comportamento della ‘‘con-vergenza prossimale’’ in soggetti strabici e normali (ri-lievi mediante determinazione al sinottoforo e conprismi). Boll Ocul 40:461, 1961.

9. Barry JC, Effert R, Kaupp A: Objective measurement ofsmall angles of strabismus in infants and children withphotographic reflection pattern evaluation. Ophthalmol-ogy 99:320, 1992.

10. Berens C, Losey CC, Hardy LH: Routine examination ofthe ocular muscles and non-operative treatment. Am JOphthalmol 10:910, 1927.

11. Bielschowsky A: Ein ungewohnlicher Fall von vertikalerHeterotopie der Makulae. Klin Monatsbl Augenheilk84:755, 1930.

12. Bielschowsky A: Disturbances of vertical motor musclesof the eyes. Arch Ophthalmol 20:175, 1938.

13. Bielschowsky A: Lectures on Motor Anomalies, Han-over, NH, Dartmouth College Publications, 1943/1956.

14. Bixenmann WW, Noorden GK von: Apparent foveal dis-placement in normal subjects and in cyclotropia. Ophthal-mologica 89:58, 1982.

15. Braun B, Schiffman EL: The validity and predictivevalue of four assessments for evaluation of the cervicaland stomatognathic systems. J Craniomandibular Disord5:239, 1991.

16. Brodie SE: Photographic calibration of the Hirschbergtest. Invest Ophthalmol Vis Sci 28:736, 1987.

17. Brown HW: The cover test. In Allen JH, ed: StrabismusOphthalmic Symposium, II. St Louis, Mosby–Year Book,1958, p 225.

18. Bruckner R: Exakte Strabismusdiagnostik bei 1/2–3 jahri-gen Kindern mit einem einfachen ‘‘Durchleuchtungs-test.’’ Ophthalmologica 144:184, 1962.

19. Burian HM: Fusional movements: The role of peripheralretinal stimuli. Arch Ophthalmol 21:486, 1939.

20. Burian HM: Fusional movements in permanent strabis-mus. A study of the role of the central and peripheralretinal regions in the act of binocular vision. Arch Oph-thalmol 26:626, 1944.

21. Burian HM: Closing remarks. In discussion of BurianHM, Spivey BE, on the surgical management of exodevi-ations. Trans Am Ophthalmol Soc 62:305, 1964.

22. Burian HM, Cahill JE: Congenital paralysis of medialrectus muscle with unusual synergism of the horizontalrectus muscles. Trans Am Ophthalmol Soc 50:87, 1952.

23. Burian HM, Van Allen MW, Sexton RR, et al: Substitu-tion phenomena in congenital and acquired supranucleardisorders of eye movement. Trans Am Acad OphthalmolOtolaryngol 69:1105, 1965.

24. Campos EC: Classification et physiopathologie du torti-collis oculaire—aspect sensoriel. Bull Soc Belge Oph-thalmol 221–222:9, 1987.

25. Campos EC, Orciuolo M, Schiavi C: A new automaticcomputerized deviometer. Int Ophthalmol 13:291, 1989.

26. Capobianco NM: The subjective measurement of the nearpoint of convergence and its significance in the diagnosisof convergence insufficiency. Am Orthopt J 2:40, 1952.

27. Capuano-Pucci D, Rheault W, Aukai J, et al: Intratesterand interester reliability of the cervical range of motiondevice. Arch Phys Med Rehabil 72:338, 1991.

28. Chavasse FB: Worth’s Squint or the Binocular Reflexesand the Treatment of Strabismus. Philadelphia, P Blakis-ton’s Son & Co, 1939.

29. Choi RY, Kushner BJ: The accuracy of experienced strab-ismologists using the Hirschberg and Krimsky tests. Oph-thalmology 105:1301, 1998.

30. Crone RA, Everhard-Halm Y: Optically induced eye tor-sion. 1. Fusional cyclovergence. Graefes Arch Clin ExpOphthalmol 195:231, 1975.

31. Cuppers C: Determination of the objective angle. InMein, J, Bierlaagh JJM, Brummelkamp-Dons TEA, eds:Orthoptics. Amsterdam, Excerpta Medica, 1972, p 65.

32. Cuppers C: Korrektur der Horizontalabweichung, vol 5.Wiesbaden, Germany, BVA Arbeitskreis Schielbehan-dlung, 1973, p 1.

33. Damms T, Damms C, Schulz E, et al: Pseudoesotropiedurch Verlangerung der Makula nach nasal bei Patientenmit infantiler hoher Myopie. Ophthalmologe 91:77, 1994.

34. DeRespinis PA, Naidu E, Brodie SE: Calibration ofHirschberg test photographs under clinical conditions.Ophthalmology 96:944, 1989.

35. Donders FC: On the Anomalies of Accommodation andRefraction of the Eye. Translated by Moore WD. London,New Syndenham Society, 1864.

36. Duane A: A new classification of the motor anomaliesof the eyes based upon physiological principles, togetherwith their symptoms, diagnosis and treatment. Reprintedfrom Ann Ophthalmol Otolaryngol 5:969, 1896.

37. Duane A, Berens C Jr: Ocular movements. OphthalmolLit 17:53, 1921.

38. du Bois-Reymond C: Ueber Schielmessung. CentralblPrakt Augenheilkd 10:5, 1886.

39. Duke-Elder S: System of Ophthalmology, vol 3, pt 2:Congenital Deformities. London, Henry Kimpton, 1964,p 851.

40. Ellerbrock VJ: Experimental investigations of verticalfusional movements. Am J Optom 26:327, 1949.

41. Ellerbrock VJ: Tonicity induced by fusional movements.Am J Optom 27:8, 1950.

42. Ellerbrock VJ: The aftereffect of aniseikonia on the am-plitude of vertical divergence. Am J Optom 29:403, 1952.

43. Ellis PP: Ectopia of the macula. Am J Ophthalmol44:262, 1957.

44. Eskridge JB, Perrigin DM, Leach NE: The Hirschbergtest: Correlation with corneal radius and axial length.Optom Vis Sci 67:243, 1990.

45. Fink WH: The vergence test—an evaluation of the vari-ous techniques. Am J Ophthalmol 31:48, 1948.

46. Franceschetti AT, Burian HM: Proximal convergence. Anevaluation by comparison of major amblyoscope andalternate prism and cover test measurements and by AC/A ratio determinations. In Strabismus ’69 Transactionsof the Consilium Europaeum Strabismi Studio DeditumCongress (London 1969). St Louis, Mosby–Year Book,1970, p 125.

47. Freedman HL, Preston KL: Polaroid photoscreening foramblyogenic factors. Ophthalmology 99:1785, 1992.

48. Fry GW, quoted by Lancaster WB: Terminology in ocularmotility and allied subjects. Am J Ophthalmol 26:122,1943.

49. Giovianni FG, Siracusano B, Cusmano R: The anglekappa in ametropia. New Trends Ophthalmol 3:27, 1988.


50. Goldstein JH, Hornblass A, Clahane AC: Effect of pe-ripheral vision on the binocular relationship: A furtherstudy. Am J Ophthalmol 66:86, 1968.

51. Graefe A von: Ueber die ophthalmoskopische Beobach-tung gewisser Augenmuskelwirkungen. Graefes ArchClin Exp Ophthalmol 2:322, 1855–1856.

52. Griffin JR, Cotter SA: The Bruckner test: Evaluation andclinical usefulness. Am J Optom Physiol Opt 63:957,1986.

53. Guibor GP: Squint and Allied Conditions. New York,Grune & Stratton, 1959.

54. Guyton DL: Remote optical systems for ophthalmic ex-aminations. Trans Am Ophthalmol Soc 84:869, 1986.

55. Guyton DL: Ocular torsion: Sensorimotor principles.Graefes Arch Clin Exp Ophthalmol 226:241, 1988.

56. Guyton DL, Moss A, Simons K: Automated measurementof strabismic deviations using a remote haploscope andan infrared television-based eye tracker. Trans Am Oph-thalmol Soc 85:320, 1987.

57. Haase W, Malchartzeck C, Rickers J: Ergebnisse derFadenoperation nach Cuppers. Klin Monatsbl Augen-heilkd 172:313, 1972.

58. Hardesty HH: Diagnosis of paretic vertical rotators. AmJ Ophthalmol 56:818, 1963.

59. Harms H: Uber die Untersuchung der Augenmuskellah-mungen. Graefes Arch Clin Exp Ophthalmol 144:129,1941.

60. Helveston EM: Two-step for diagnosing paresis of verti-cally acting extraocular muscle. Am J Ophthalmol64:914, 1967.

61. Herzau W: Bestimmung der Medianabweichung desAuges. Klin Monatsbl Augenheilkd 86:406, 1931.

62. Hess WR: Ein einfaches messendes Verfahren zur Motili-tatsprufung der Augen. A Augenheilkd 35:201, 1916.

63. Hirschberg J: Uber die Messung des Schielgrades unddie Dosierung der Schieloperation. Zentralbl Prakt Auge-nkeilkd 9:325, 1885.

64. Hofmann FB, Bielschowsky A: Die Verwertung derKopfneigung zur Diagnose der Augenmuskellahmungen.Graefes Arch Clin Exp Ophthalmol 51:174, 1900.

65. Hofmann FB, Bielschowsky A: Uber die der Willkurentzogenen Fusionsbewegungen der Augen. PflugersArch 80:1, 1900.

66. Javal E: Manuel du strabisme. Paris, Masson, 1896, p 55.67. Kertesz AE, Sullivan MJ: The effect of stimulus size on

human cyclofusional response. Vision Res 18:567, 1978.68. Kestenbaum A: Clinical Methods of Neuro-Ophthalmo-

logic Examination, ed 2. New York, Grune & Stratton,1961, p 237.

69. Krimsky E: The binocular examination of the youngchild. Am J Ophthalmol 26:624, 1943.

70. Kushner BJ: The usefulness of the cervical range ofmotion device in the ocular motility examination. Oph-thalmology 118:946, 2000.

71. Lancaster WB: Detecting, measuring, plotting and inter-preting ocular deviations. Trans Section OphthalmolAMA 90th session, 1939, p 78.

72. Lancaster WB: Terminology in ocular motility and alliedsubjects. Am J Ophthalmol 26:122, 1943.

73. Lancaster WB: Personal communication, quoted byRoper, KN, Bannon RE: Diagnostic values of monocularocclusion. Arch Ophthalmol 51:316, 1944.

74. Lancaster W: Refraction Correlated with Optics andPhysiological Optics and Motility Limited to Heteropho-ria. Springfield, IL, Charles C Thomas, 1952, p 102.

75. Lang J: The fourth image of Purkinje: A diagnostic toolin microtopia. Doc Ophthalmol 58:91, 1984.

76. Locke JC: Heterotopia of the blind spot in ocular verticalmuscle imbalance. Am J Ophthalmol 65:362, 1968.

77. Ludvigh E: Amount of eye movement objectively percep-tible to the unaided eye. Am J Ophthalmol 32:649, 1949.

78. Lyle TK, Wybar KC: Lyle and Jackson’s practical or-thoptics in the treatment of squint (and other anomaliesof binocular vision), ed 5. Springfield, IL, Charles CThomas, 1967.

79. Mackensen G: Die Tangentenskala nach Harms. InAugenmuskellahmungen. Bucherei d. Augenarztes, vol46. Stuttgart, Ferdinand Enke Verlag, 1966.

80. Marlow FW: Prolonged monocular occlusion as a test formuscle balance. Am J Ophthalmol 4:238, 1921.

81. Mehdorn E, Kommerell G: ‘‘Rebound saccade’’ in theprism cover test. Int Ophthalmol 1:63, 1978.

82. Mellick A: Convergence. An investigation into the nor-mal standards of age groups. Br J Ophthalmol 33:725,1949.

83. Miles DR, Burian HM: Unpublished case observed inthe Department of Ophthalmology, University of Iowa,Iowa City.

84. Miller JM, Hall HL, Greivenkamp JE, et al: Quantifica-tion of the Bruckner test for strabismus. Invest Ophthal-mol Vis Sci 36:897, 1995.

85. Muhlendyck H: Der Synoptometer als Grundlage vonOperationsindikationen und Verlaufskontrolle bei kompli-zierten Augenmuskelstorungen. Klin Monatsbl Augen-heilkd 167:892, 1975.

86. Muhlendyck H, Linnen HJ: Die operative Behandlungnystagmusbedingter schwankender Schielwinkel mit derFadenoperation nach Cuppers. Klin Monatsbl Augen-heilkd 167:273, 1975.

87. Neikter B: Effects of diagnostic occlusion on ocularalignment in normal subjects. Strabismus 2:67, 1994.

88. Noorden GK von, Olson CL: Diagnosis and surgicalmanagement of vertically incomitant horizontal strabis-mus. Am J Ophthalmol 60:434, 1965.

89. Ogle KN: Distortion of the image by prisms. J Opt SocAm 41:1023, 1951.

90. Olivier P, Noorden GK von: Excyclotropia of the nonpa-retic eye in unilateral superior oblique muscle paralysis.Am J Ophthalmol 93:30, 1982.

91. Ottar WL, Scott WE, Holgado LI: Photoscreening foramblyogenic factors. J Pediatr Ophthalmol Strabismus32:289, 1995.

92. Paliaga GP: Linear strabismometric methods. BinocularVision 7:139, 1992.

93. Paliaga GP, Ghisofi A, Guinta G, et al: Millimetric covertest—a linear strabismometric technique. J Pediatr Oph-thalmol Strabismus 17:331, 1980.

94. Paliaga GP, Paliaga A, Decarli A: Evaluation of ocularrotation by measurement of corneal light reflex move-ments. Clin Oculistica Patol Ocul 6:449, 1983.

95. Parkinson DK, Burke JP, Shipman TL: Normal fusionalamplitudes: With special attention paid to cyclofusion. InLennerstrand G, ed: Advances in Strabismology. Pro-ceedings of the Eighth Meeting of the InternationalStrabismological Association, Maastricht, The Nether-lands, Sept 10–12, 1998. Buren, The Netherlands, AeolusPress, 1999, p 95.

96. Parks MM: Isolated cyclovertical muscle palsy. ArchOphthalmol 60:1027, 1958.

97. Putnam OA, Quereau JV: Precisional errors in measure-ment of squint and phoria. Arch Ophthalmol 34:7, 1945.

98. Romano PE, Noorden GK von: Limitations of cover testin detecting strabismus. Am J Ophthalmol 77:10, 1971.

99. Roper KN, Bannon RE: Diagnostic values of monocularocclusion. Arch Ophthalmol 31:316, 1944.

100. Ruttum M, Noorden GK von: Adaptation to tilting of thevisual environments in cyclotropia. Am J Ophthalmol96:229, 1983.

101. Ruttum M, Noorden GK von: The Bagolini striated lenstest for cyclotropia. Doc Ophthalmol 58:131, 1984.

102. Ruttum MS, Shimshak KJ, Chesner M: Photographic


measurement of the angle of strabismus. In Campos ES,ed: Strabismus and Motility Disorders. Proceedings ofthe Sixth Meeting of the International StrabismologicalAssociation. London, Macmillan, 1990, p 155.

103. Scattergood KD, Brown M, Guyton D: Artifacts intro-duced by spectacle lens in the measurement of strabismicdeviations. Am J Ophthalmol 96:439, 1983.

104. Schatz H: An instrument for measuring ocular torticollis(head turn, tilt, and bend). Am Acad Ophthalmol Otol75:650, 1971.

105. Schworm HD, Kau C, Reindl B, et al: Zur Fruherkennungamblyopieauslosender Augenveranderungen. Klin Mon-tatsbl Augenheilkd 21:158, 1997.

106. Scobee RG: The Oculorotary Muscles, ed 2. St LouisMosby–Year Book, 1952.

107. Sethi B, Henson DB: Adaptive changes with prolongedeffect of comitance and incomitance vergence disparities.Am J Optom Physiol Opt 61:505, 1984.

108. Sharma K, Abdul-Rahim AS: Vertical fusion amplitudein normal adults. Am J Ophthalmol 114:636, 1992.

109. Simon K, Arnoldi K, Brown MH: Color dissociationartifacts in double Maddox rod cylcodeviation testing.Ophthalmology 101:1897, 1994.

110. Simons BD, Siatkowsky RM, Schiffman JC, et al: Pediat-ric photoscreening for strabismus and refractive errors ina high-risk population. Ophthalmology 106:1073, 1999.

111. Sloane AE: Analysis of methods for measuring diplopiafields. Introduction of device for such measurements.Arch Ophthalmol 46:277, 1951.

112. Spielmann A: A translucent occluder for study of eyeposition under unilateral or bilateral cover test. Am Or-thopt J 36:65, 1986.

113. Spierer A: Measurement of cyclotorsion. Am J Ophthal-mol 122:911, 1996.

114. Sradj N: Uber die Bedeutung ocular bedingter Zwangs-haltungen und die Moglichkeit ihrer Messung mit demTorticollometer. Klin Monatsbl Augenheilk 1656:823,1974.

115. Sradj A: Torticollometry for direct measurement of headposition. Am Orthopt J 34:117, 1984.

116. Tait EF: Fusional vergence. Am J Ophthalmol 32:1223,1949.

117. Thompson DA: Measurements with cover test vs. tropo-scope. Am Orthoptics J 2:47, 1952.

118. Thompson JT, Guyton DL: Ophthalmic prisms: Measure-ment errors and how to minimize them. Ophthalmology90:204, 1983.

119. Toosi SH, Noorden GK von: Effect of isolated inferioroblique muscle myectomy in the management of superioroblique muscle palsy. Am J Ophthalmol 88:602, 1979.

120. Tong PY, Enke-Miyazaki E, Bassin RE, et al: Screeningfor amblyopia in preverbal children with photoscreeningphotographs. National Children’s Eye Care FoundationVision Screening Study Group. Ophthalmology 105:856,1998.

121. Tschermak-Seysenegg A von: Introduction to Physiologi-cal Optics. Translated by Boeder P. Springfield, IL,Charles C Thomas, 1952, p 140.

122. Tscherning H: Optique physiologique. Paris, GeorgesCarre et C. Naud, 1898, p 42.

123. Urist MJ: Lateral version light reflex test. Am J Ophthal-mol 63:808, 1967.

124. Urist MJ: Head tilt in vertical muscle palsy. Am J Oph-thalmol 69:970, 1970.

125. Weinand F, Graf M, Denning K: Sensitivity of the MTIphotoscreener for amblyogenic factors in infancy andearly childhood. Graefes Arch Clin Exp Ophthalmol236:801, 1998.

126. Wiesinger: Neuere Methoden der Schielbehandlung. Ge-sellschaft Charite Aerzte. Report of meeting of May 10,1906. Klin Wochenschr 43:1025, 1906.

127. Worth C, cited by Bruckner R: Exakte Strabismusdiag-nostik bei 1/2–3 jahrigen Kindern mit einem einfachen‘‘Durchleuchtungstest.’’ Ophthalmologica 144:184, 1962.

128. Young JD: Head posture measurement. J Pediatr Ophthal-mol Strabismus 25:86, 1988.

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