After the Eyes are Straightened what is the Ophthalmologist's Responsibility? MARSHALL M. PARKS, MD

Abstract: Occlusion, glasses, prism therapy, miotics, fusional vergence stim­ulation, plus more surgery are required frequently in various combinations for a high percentage of patients whose strabismic eyes are straightened by surgery. Amblyopia is a serious sequalae befalling children who are dismissed following satisfactory surgery. Their best possible postoperative status is monofixation (absence of bifixation), despite having straight eyes. Unless they alternate fix­ation, amblyopia is prone to either occur or recur. Also, either a gradual change in motor innervation to the extraocular muscles or a cicatricial scarring process may subtly cause subsequent strabismus. Hence, despite straight eyes post­operatively the surgeon's responsibility continues. [Key words: amblyopia, monofixation syndrome, strabismus surgery.] Ophthalmology 93: 1 020-1 022, 1986

The objective of strabismus therapy is to straighten the eyes. Once the objective has been accomplished, the re­ponsibility of the ophthalmologist becomes one of mon­itoring the visual acuity, refraction, alignment and mo­tility.

AMBLYOPIA MONITORING

Children younger than 9 years of age require close at­tention to the developing fixation reflex or visual acuity in each eye. Amblyopia remains a threat during this pe­riod, despite the eyes having been straightened. The prob­ability for amblyopia varies among strabismus types. However, one common denominator prevails throughout all strabismus types: the monofixating patient is at risk for amblyopia. The majority of strabismus patients, with

Presented at an Annual Meeting of the American Academy of Ophthal· mology.

Reprint requests to Marshall M. Parks, MD, 3400 Massachusetts Avenue NW, Washington, DC 20007.

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the exception of certain strabismus types, are monofixators despite their eyes having been straightened.

Bifixation is a tenuous reflex, demanding continuous use if it is not to be lost forever. Unlike extramacular (peripheral) single binocular vision, the reflex serving macular (central) single binocular vision ceases to function wh(!n the eyes become tropic. Extramacular binocular vi­sion continues during tropia but in time the youngster adapts suppression and anomalous retinal correspondence (ARC) to eliminate the annoying diplopia and visual con­fusion. The older person simply continues with the both­ersome diplopia and confusion as the reflex serving ex­tramacular binocular vision functions, despite long-lasting acquired tropia. Macular single binocular vision (bifixa­tion) is lost forever after two to three months of not using this reflex. Clinical examples abound to support this ob­servation. For example, the intermittent exotropic patient with bifixation and 40 seconds of arc stereoacuity while phoric, loses bifixation forever if permitted to remain constantly esotropic for two to three months after over­corrective surgery. The traumatic monocular cataract pa­tient undergoes the same permanent change if not visually rehabilitated in only a few weeks after injury. Constant

PARKS • RESPONSIBILITY

strabismus that has replaced intermittent strabismus, therefore becomes a very amblyogenicfactor which must be contended with after the eyes are straightened. More importantly, the duration of the acquired constant stra­bismus prior to straightening of the eyes becomes the im­portant fact for prognosticating the risk for amblyopia after eliminating the tropia. Three months of constant acquired strabismus results in no chance for restoration of bifixation.

Patients with congenital constant strabismus, such as the congenital esotrope, or the congenital exotrope, never bifixate after their eyes are straightened, even though sur­gical alignment is accomplished by, or prior to, six months of age. I have managed only one congenitally esotropic patient who proved to be the exception to this generality.' The risk for amblyopia to occur after the eyes are straight­ened is less for the congenitally strabismic patients than for the acquired strabismic patients. However, amblyopia does occur postoperatively in some of these patients, al­though it did not exist preoperatively. For example, the majority of the congenital esotropes alternately fixate and cross fixate prior to surgery. However, they do not nec­essarily continue the same fixating pattern after the eyes are straightened. Now, the patient is more inclined to fix­ate exclusively with one or the other eye, ultimately man­ifesting amblyopia in the nondominant eye.

A large group of patients with excellent prognosis for bifixation after their eyes were straightened are intermit­tent exotropes. Another large group with similar excellent prognosis for bifixation after treatment is begun are the recently acquired accommodative esotropes, particularly when still intermittently phoric. A small group with ex­cellent prognosis for bifixation are the cyclic esotropic patients. Other groups of patients with strabismus re­stricted to certain fields of gaze, such as Duane's syn­drome, Brown's syndrome, oblique muscle dysfunctions, and partial third, fourth, or sixth cranial nerve palsies tend to bifixate prior to surgery in certain gaze positions and continue bifixation after straigthening their eyes.

Regardless of the strabismus type, if the patient is treated for amblyopia prior to straightening of the eyes, the risk is high for amblyopia return.

REFRACTION MONITORING

The refraction usually changes in growing children. The change can be large and evolve into a significant aniso­metropia, which in a young child can become an ambly­ogenic factor.

A good rule to enforce in the management of young children is invariably to repeat the cycloplegic refraction annually, even after their eyes have been straightened.

The quantity of hypermetropia is subject to changing with age. Usually the hypermetropia increases until ap­proximately 5 years of age and decreases after 8 years of age. Consequently, the accommodative esotropic child requires annual cycloplegic refraction. These patients' best

control of alignment and visual acuity frequently demands adjustment of the lens power according to the optical change recorded by the annual cycloplegic refraction.

ALIGNMENT MONITORING

Never can the ophthalmologist conclude, regardless of the patient's age, that once the treatment has successfully aligned the strabismic eyes they will remain straight. All patients deserve follow-up examinations to investigate their ability to stay satisfactorily aligned over time. The ophthalmologist's responsibility never ceases in this re­spect.

Esotropic patients once aligned tend to restore to eso­tropia with certain noteable exceptions. One exception is the patient whose accommodative esotropic eyes were in­judiciously aligned with surgery instead of plus lenses. Sooner or later, this temporarily successful alignment is replaced with exotropia that relentlessly increases with time. Another exception are older patients with congenital esotropia and no single binocular vision capability, whose eyes appear straight for awhile after surgery. However, in the absence of extramacular fusional vergences, the align­ment gradually erodes into ever increasing exotropia. Generally, however, if any postoperative alignment change occurs, the esotropic patients tend to return to esotropia, the exotropic patients tend to return to exotropia, and the hypertropic patients tend to return to their preoper­ative type of hypertropia.

The congenitally esotropic children, straightened by surgery prior to their second birthday, tend to develop accommodative esotropia between two and three years of age. In fact, 55% of the congenitally esotropic patients aligned by surgery during their first year oflife developed accommodative esotropia later and required plus spherical spectacles to keep their eyes straight.2

Also, the congenitally esotropic patient is peculiar in respect to a vertical disorder that often affects the align­ment after the eyes are straightened. Dissociated vertical deviation usually appears after 2 years of age and may eventually become cosmetically disfiguring requiring sur­gery. About 90% of the congenital esotropes will develop the hypertropia, but only about one in three have sufficient degree of the disorder to need treatment by surgery.

MOTILITY MONITORING

Although the eyes have been aligned and all is well in the primary position, children have a propensity to grad­ually develop oblique muscle dysfunction. Either the in­ferior oblique muscles or superior oblique muscles begin to overact. Often an associated V or A pattern appears along with the oblique muscle overaction. The oblique muscle dysfunction may first appear within months or

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OPHTHALMOLOGY • AUGUST 1986 • VOLUME 93 • NUMBER 8

several years after primary position alignment is achieved; the dysfunction may be symmetrical or asymmetrical, ranging from maximal to severe. Every six months to a year the straightened strabismic child should have motility assessed by having the eyes moved into the cardinal fields and midline up- and downgaze.

Other defects in motility may gradually become ap­parent other than oblique muscle dysfunction. Scarring in the operative sites, adherence syndrome, and slipped muscles may first be manifest by motility restrictions al­though the eyes remain straight in the primary position.

The job is not completed after the eyes are aligned. Amblyopia, refraction, alignment and motility monitoring are required after the eyes have been straightened. Concern about amblyopia continues after 9 years of age, but re-

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fraction monitoring persists through the second decade. Alignment and motility monitoring by the ophthalmol­ogist never ends after rendering strabismus care. No matter how satisfactory the result appears, the patient is told to return after some specified interval because a change may occur.

REFERENCES

1. Parks MM. Congenital esotropia with a bifixation result; report of a case. Doc Ophthalmol1984; 58:109-14.

2. Parks MM, Mitchell PRo Concomitant exodeviations. In: Duane TO, ed. Clinical Ophthalmology, revised ed. Philadelphia: Harper & Row, 1985; Volume 1, Chapter 13:11.