Esotropia is an eye misalignment in which one eye is deviated inward, or nasally. The deviation may be constant or intermittent. The deviating eye may always be the same eye or may alternate between the two eyes.
This is an esodeviation, often constant, that presents in the first 12 months of life. It is associated with a large angle deviation, latent nystagmus, a crossfixation pattern of fixation, a normal accommodative convergence to accommodation ratio, and age-appropriate refractive errors.
The onset is usually after 1 year of age with a gradual or sudden onset becoming constant after a period of intermittency. Fully accommodative esotropia is associated with high hyperopia of +3.00 D or greater and inadequate fusional divergence amplitudes.
A subtype of accommodative esotropia is convergence excess type esotropia, which is associated with a deviation greater at near than distance. The deviation at near is reduced when accommodation is relaxed with +3.00D lenses. The mechanism is an abnormal ratio between accommodative convergence and accommodation (high accommodative convergence to accommodation ratio); the effort to accommodate elicits an abnormally high accommodative convergence response. Partially accommodative esotropia is a residual esotropia that is partially corrected, yet still persists in spite of full correction of hyperopic refractive error.
This esodeviation has an onset after 1 year of age, and is not associated with any accommodative factor, therefore not improved by glasses.
Divergence insufficiency type esotropia
This esotropia, most often associated with adult patients 30 years and older, is characterized by an esodeviation greater at distance than near. Fusional divergence amplitudes are reduced at both distance and near fixation, and this esotropia is comitant in primary and lateral gazes.
This is characterized by patients with a central scotoma in one eye together with peripheral fusion. These patients typically lack fine stereopsis and maintain a mild to moderate degree of fusional amplitudes.
Unilateral reduced visual acuity, due to various organic causes, presents a barrier to fusion. In children under 4 years of age, the blind or poorer-seeing eye will generally become esotropic. Older children or adults with sensory visual deprivation will generally develop a sensory exotropia.
This occurs when a person who was formerly exotropic becomes esotropic. Sometimes this is a result of surgical overcorrection for exotropia.
Esotropia associated with restrictive myopathy (thyroid eye disease, orbital fractures) or paralytic myopathy (6th cranial nerve palsy, myastenia gravis), special forms of strabismus- Duane's syndrome
The etiology of esotropia is unknown in most cases, but it can be hereditary. Sensory esotropia occurs because of decreased acuity in one eye, due to various organic causes, which leads to an inability to maintain normal eye alignment. It is thought that strabismus occurs because of a problem with the fusional system.
Neurological disorders, hydrocephalus, prematurity, and a positive family history of strabismus increase the risk of having esotropia.
Accommodative esotropia is the most common subtype of esotropia, with an onset after 1 year of age and usually detected around 2-3 years of age. There is no predilection for esotropia in terms of age or gender.
All patients with esotropia would need a complete ophthalmologic examination, including visual acuity, binocular function and stereopsis, motility evaluation, strabismus measurements at near, distance, and cardinal positions of gaze, measurement of fusional amplitudes, cycloplegic refraction. Some cases may require a 4 prism diopter base out test for microtropia, strabismus measurements after Marlowe’s prolonged occlusion test, strabismus measurements after +3.00 lenses at near fixation, evaluation of ocular structures in the anterior and posterior segments.
Symptoms are quite variable in terms of frequency and severity of the esotropia. If a child suppresses the deviated eye, the patient can develop an amblyopia or a more severe angle or frequency of the strabismus. Adults with esotropia may experience diplopia.
An infant with an esotropia that is usually constant and presents within the first one year of life. It is associated with a large angle deviation, latent nystagmus, crossfixation, a normal accommodative convergence to accommodation ratio, and age-appropriate refractive errors.
Occurs in children over 1 year of age. In general, this is associated with hyperopia which reduces the angle and/or frequency of the esotropia when the hyperopic correction is worn. Accommodative esotropia may also be associated with microtropia/monofixation syndrome.
This subtype has an onset after 1 year of age, can be constant or intermittent, and is not affected by the level of accommodation.
Divergence insufficiency type esotropia
This type of esotropia is found in the population 30 years of age and above. These patients have reduced fusional divergence amplitudes, the esotropia is worse at distance than near, and they may have trouble with driving or diplopia with distance fixation.
This is characterized by patients with a central scotoma in one eye together with peripheral fusion, fusional amplitudes, and gross stereopsis.
Other conditions that can display esotropia include Duane Syndrome types 1 or 3, 6th CN palsy, Nystagmus blockage syndrome, Moebius syndrome, thyroid eye disease, Myasthenia gravis, congenital fibrosis of the extraocular muscles, slipped lateral rectus muscle, or tight medial rectus muscle.
Nonsurgical treatments include patching, correction of full hyperopic refractive error, and divergence orthoptic exercises for divergence insufficiency. Fresnel prisms or prism glasses can be used to relieve diplopia or asthenopia in certain patients. Sometimes sensory esotropia can be helped by treating the underlying cause (amblyopia, cataract, media opacity).
Surgery is performed on the extraocular muscles in an attempt to give binocular single vision, to relieve diplopia, or to restore the eyes to their regular state of alignment. The prognosis for surgical success is best if the patient has an intermittent esotropia rather than a constant one, and alternating esotropia, and if any amblyopia is treated. In certain cases, amblyopia may not be fully corrected due to the strabismus, and surgery may be needed prior to full correction of the amblyopia. The optimal time for surgical intervention is as early as possible, within a few months of the onset, prior to any degenerations of the lateral geniculate nucleus. In case of associated amblyopia it is recommended to treat it prior to surgery to improve the long-term success rate of eye alignment.
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