Page 2 of 10 PREVIOUS | NEXT

Print this Page Print this Chapter ( K)

ESOTROPIA (Convergent Strabismus, "Crossed Eyes")

Esotropia is by far the most common type of strabismus. It is divided into two types: paretic (due to paresis or paralysis of one or both lateral rectus muscles) and nonparetic (comitant). Nonparetic esotropia is the most common type in infants and children; it may be accommodative, nonaccommodative, or partially accommodative. Paretic strabismus is uncommon in childhood but accounts for most new cases of strabismus in adults. Most cases of childhood nonaccommodative esotropia are classified as infantile esotropia, with onset by age 6 months. The remainder occur after age 6 months and are classified as acquired nonaccommodative esotropia.

NONPARETIC ESOTROPIA

Nonaccommodative Esotropia

A. Infantile Esotropia:

Nearly half of all cases of esotropia fall into this group. In most cases, the cause is obscure. The convergent deviation is manifest by age 6 months. The deviation is comitant, ie, the angle of deviation is approximately the same in all directions of gaze and is usually not affected by accommodation. The cause, therefore, is not related to the refractive error or dependent upon a paretic extraocular muscle. It is likely that the majority of cases are due to faulty innervational control, involving the supranuclear pathways for convergence and divergence and their neural connections to the medial longitudinal fasciculus. A smaller number of cases are due to anatomic variations such as anomalous insertions of horizontally acting muscles, abnormal check ligaments, or various other fascial abnormalities.

There is also good evidence that strabismus does occur on a genetically determined basis. Esophoria and esotropia are frequently passed on as an autosomal dominant trait. Siblings may have similar ocular deviations. An accommodative element is often superimposed upon comitant esotropia, ie, correction of the hyperopic refractive error reduces but does not eliminate all of the deviation.

The deviation is often large ( 40^Δ). Abduction may be limited but can be demonstrated. Vertical deviations may be observed after 18 months of age as a result of overaction of the oblique muscles or dissociated vertical deviation. Nystagmus, manifest or latent, may be present. The most common refractive error is low to moderate hyperopia.

The eye that appears to be straight is the eye used for fixation. Almost without exception, it is the eye with better vision or lower refractive error (or both). If there is anisometropia, there will probably be some amblyopia as well. If at various times either eye is used for fixation, the patient is said to show spontaneous alternation of fixation; in this case, vision will be equal or nearly equal in both eyes. In some cases, the eye preference is determined by the direction of gaze. For example, with large-angle esotropia, there is a tendency for the right eye to be used in left gaze and the left eye in right gaze (cross fixation).

Infantile esotropia is treated surgically. Preliminary nonsurgical treatment may be indicated to ensure the best possible result. It is essential that amblyopia be fully treated prior to surgery. Glasses should be tried in hyperopic refractive errors of 3 D or more to determine if reducing accommodation has a favorable effect on the deviation. A myotic may be used successfully as an alternative to glasses if the refractive error is not above approximately 4 D.

Surgery is usually indicated after medical therapy and treatment of amblyopia have been completed. Once reproducible measurements are obtained, surgery should be performed since there is ample evidence that sensory results are better the sooner the eyes are aligned. Many procedures have been recommended, but the two most popular are (1) weakening of both medial rectus muscles, and (2) recession of the medial rectus and resection of the lateral rectus on the same eye.

B. Acquired Nonaccommodative Esotropia:

This type of esotropia develops in childhood, usually after the age of 2 years. There is little or no accommodative factor. The angle of strabismus is often smaller than in infantile esotropia but may increase with time. Otherwise, clinical findings are the same as for congenital esotropia. Treatment is surgical and follows the same guidelines as for congenital esotropia.

Accommodative Esotropia

Accommodative esotropia occurs when there is a normal physiologic mechanism of accommodation with an associated overactive convergence response but insufficient relative fusional divergence to hold the eyes straight. There are two pathophysiologic mechanisms at work, singly or together: (1) sufficiently high hyperopia, requiring so much accommodation (and therefore convergence) to clarify the image that esotropia results; and (2) a high AC/A ratio, which is accompanied by mild to moderate hyperopia (1.5 D or more).

A. Accommodative Esotropia Due to Hyperopia:

Accommodative esotropia due to hyperopia typically begins at age 2-3 but may occur earlier or later. Deviation is variable prior to treatment. Glasses with full cycloplegic refraction allow the eyes to become aligned

B. Accommodative Esotropia Due to High AC/A Ratio:

In accommodative esotropia due to a high ratio of accommodative convergence to accommodation (AC/A ratio), a deviation is greater at near than at distance. The refractive error is hyperopic. Treatment is with glasses with full cycloplegic refraction plus bifocals or miotics to relieve excess deviation at near.

Partially Accommodative Esotropia

A mixed mechanism-part muscular imbalance and part accommodative/convergence imbalance-may exist. Although antiaccommodative therapy decreases the angle of deviation, the esotropia is not eliminated. Surgery is performed for the nonaccommodative component of the deviation with the choice of surgical procedure as described for infantile esotropia.

PARETIC (INCOMITANT) ESOTROPIA (Abducens Palsy) (  Figures 12-2 and   12-9)

Incomitant strabismus results from paresis or restriction of action of one or more extraocular muscles. Incomitant esotropia is usually due to paresis of one or both lateral rectus muscles as a result of unilateral or bilateral abducens nerve palsy (see Chapter 14). Other causes are fracture of the medial orbital wall with entrapment of the medial rectus muscle, dysthyroid eye disease with contracture of the medial rectus muscles, and Duane's retraction syndrome (see below). Abducens nerve palsy is most frequently seen in adults with systemic hypertension or diabetes, in which case spontaneous resolution usually begins within 3 months. Abducens palsy may also be the first sign of intracranial tumor or inflammatory disease. Associated neurologic signs are then important clues. Head trauma is another frequent cause of abducens palsy.

Incomitant esotropia is also seen in infants and children, but much less commonly than comitant esotropia. These cases result from birth injuries affecting the lateral rectus muscle directly, from injury to the nerve, or, less commonly, from a congenital anomaly of the muscle or its fascial attachments.

Esotropia is characteristically greater at distance than at near and greater to the affected side. Paresis of the right lateral rectus causes esotropia that becomes greater on right gaze and, if paresis is mild, little or no deviation on left gaze. If the lateral rectus muscle is totally paralyzed, the eye will not abduct past the midline.

Acquired abducens palsy is initially managed by occlusion of the paretic eye or with prisms. Botulinum toxin type A injections into the antagonist medial rectus muscle may provide symptomatic relief but do not appear to influence the final outcome. If lateral rectus function in incomplete palsies has not recovered after 6 months, medial rectus botulinum toxin type A injections may be used on a long-term basis to allow fusion-and hence abolition of diplopia-in straight-ahead gaze or to facilitate prism therapy. Horizontal rectus muscle surgery, involving resection of one or both lateral recti and recessions of the medial recti, may also be valuable. Adjustable sutures are useful in achieving the largest possible area of binocular single vision. In complete palsies that have failed to improve after 6 months, surgical transposition of the insertions of the superior and inferior rectus muscles to the insertion of the lateral rectus muscle, combined with temporary paralysis of the medial rectus muscle by botulinum toxin type A, produces the best results. Abduction cannot be restored, but fusion in primary position, with or without the aid of prisms, and a reasonable field of binocular single vision can usually be achieved.

Pseudoesotropia

Pseudoesotropia is the illusion of crossed eyes in an infant or toddler when no strabismus is present. This appearance is usually caused by a flat, broad nasal bridge and prominent epicanthal folds that cover a portion of the nasal sclera, giving the impression that the eyes are crossed. This very common condition may be differentiated from true misalignment by the corneal light reflection appearing in the center of the pupil of each eye when the child fixates a light. With normal facial growth and increasing prominence of the nasal bridge, this pseudoestropic appearance gradually disappears. Of course, true esotropia may be present in association with this common infantile facial configuration.

10.1036/1535-8860.ch12

Customer Privacy Policy Copyright ©2002-2003 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use and Notice. Additional credits and copyright information. For further information about this site contact tech_support@accessmedicine.com. Last modified: October 17, 2002 .