dr. JagdiSh duKreCoNSultaNt

Shree KruShNa Netralay

Strabismus or squint or simply deviation of the eye refers to a misalignment of the visual axis.

Strabismus originates from the Greek. Strabismus originates from the Greek.

Hippocrates used the word streblos, ‘‘turned,’’ ‘‘twisted,’’ when he talked about strabismic subjects and the word is derived from the verb strephein, ‘‘to twist,’’ ‘‘to turn.’’

No classification is perfect or all-inclusive, and several methods of classifying eye alignment and motility disorders are used. Following are terms used in these classifications.

1. Fusional Status 1. Fusional Status 2. Type of Deviation3. Variation of the Deviation With Gaze Position or Fixating Eye4. Fixation5. Age of Onset6. Depending upon the Etiology

1. Phoria A latent deviation in which fusional control is always present.

2. Intermittent Tropia A deviation in which fusional control is present part of the time.present part of the time.

3. Tropia A manifest deviation in which fusional control is not present.

Heterophoria, the term introduced by Stevens, refers to a condition in which the tendency of the eyes to deviate is overcome (kept latent) by the fusion reflex during binocular vision.

Therefore, when the influence of fusion is interrupted, the visual axis of the non-fixing eye deviates from the orthoposition.axis of the non-fixing eye deviates from the orthoposition.

Depending upon the direction of deviation, heterophoria may be classified into:

1. Esophoria2. Exophoria3. Right hyperphoria4. Left hyperphoria5. Incyclophoria6. Excyclophoria

Horizontal Esodeviation or exodeviation

Vertical Hyperdeviation or hypodeviation Vertical Hyperdeviation or hypodeviation

Torsional Incyclodeviation or excyclodeviation

Combined Horizontal, vertical, torsional, pattern or any combination thereof

1. Comitant (concomitant)

The size of the deviation does not vary by more than a few prism diopters with direction of gaze or with the eye few prism diopters with direction of gaze or with the eye used for fixating.

2. Incomitant (noncomitant) The deviation varies in size with the direction of gaze or

with the eye used for fixating. Most incomitant strabismus is paralytic or restrictive.

Alternating Spontaneous alternation of fixation from one eye to the other.

Monocular Definite preference for fixation with one eye

Congenital A deviation documented before age 6 months. presumably related to a defect present at birth; the term infantile might be more appropriate.birth; the term infantile might be more appropriate.

Acquired A deviation with later onset after a period of apparently normal visual development.

Primary heterotropia

Accommodative heterotropia

Secondary/sensory heterotropia Secondary/sensory heterotropia

Consecutive heterotropia

Paralytic strabismus

Mechanical-Restrictive Strabismus

Orbital Strabismus

Wherein no obvious cause is found, Duane suggested following

terms:

1. Convergence excess type of esodeviation which is more for near

than distance fixation.than distance fixation.

2. Divergence insufficiency type of esodeviation which is more for

distance fixation than the near.

3. Convergence insufficient type of exodeviation which is more for

near fixation than the distance.

4. Divergence excess type of exodeviation which is more for

distance fixation than near.

Accommodative heterotropia In it, act of accommodation has a major influence on the

deviation.

Secondary/sensory heterotropiaSecondary/sensory heterotropia It is used to describe a deviation which results from some known

cause of visual deprivation/ sight impairing disease of one eye, e.g. anisometropia, central chorioretinitis, etc.

Consecutive heterotropia It is used to describe the deviation resulting from surgical

overcorrection or spontaneous conversion of an esotropic eye into an exodeviation.

The term paralytic strabismus is limited to an innervational cause of restricted motility.

The terms N III, N IV, and N VI paralysis refer to paralyses of muscles supplied by those cranial nerves. of muscles supplied by those cranial nerves.

If all extraocular muscles supplied by the third cranial nerve are paralyzed, the paralysis is termed a complete oculomotor palsy; if one or more extraocular muscles are spared, the oculomotor palsy is partial.

If all extraocular muscles are paralyzed, it is called an external ophthalmoplegia.

If the intrinsic ocular muscles are paralytic, it is internal ophthalmoplegia.

If both the extrinsic and intrinsic ocular muscles are affected, then complete ophthalmoplegia occurs.

Mechanical-Restrictive StrabismusMechanical-Restrictive Strabismus Structural alteration of the muscle itself or of its antagonist may

limit its ability to function normally.

Orbital Strabismus Any ocular misalignment caused by anomalies of the orbit or of the

face may be referred to as orbital strabismus. E.g. (craniofacial dysostoses, plagiocephaly, hydrocephalus, heterotopia of muscle pulleys, etc)

Binocular Vision and Ocular Motility, Gunter K. von Noorden, Chapter 8 Classification of Neuromuscular Anomalies of the Eyes

Pediatric Ophthalmology and Strabismus, AAO Chapter 1: Pediatric Ophthalmology and Strabismus, AAO Chapter 1: Strabismus Terminology.

Theory and Practice of Squint & Orthoptics, A K Khurana, Chapter 5 Strabismus: Definition, Classification and Etiology.