Background
Strabismus is misalignment of the eyes such that both eyes are not simultaneously directed at the same object. Esotropia is a type of strabismus characterized by an inward deviation of one eye relative to the other eye. Accommodative esotropia is an esodeviation due to normal accommodation in uncorrected hyperopia. It is often hereditary, occasionally occurs with diplopia, and is sometimes brought on by trauma or illness. [1]
Pathophysiology
Types of accommodative esotropia include refractive accommodative esotropia, high AC/A (accommodative convergence/accommodation) ratio accommodative esotropia, and partially accommodative esotropia. The AC/A (accommodative convergence/accommodation) ratio gives the relationship between the amount of convergence (in-turning of the eyes) that is generated by a given amount of accommodation (focusing effort). Accommodative esotropia is frequently associated with amblyopia. Amblyopia is reduced visual acuity due to an abnormal visual experience early in life. [1]
Refractive accommodative esotropia requires a patient with uncorrected hyperopia to accommodate to clear a blurred retinal image. This process of accommodation will stimulate convergence and strain fusional divergence. When fusional divergence is insufficient, the eyes cross. The patient with uncorrected hyperopia can see either a single blurred image or a double image in which one image is clear and one image is blurred. Over time, the blurred image can be suppressed; fixation can alternate; or, more commonly in the setting of accommodative esotropia, amblyopia can occur.
High AC/A ratio accommodative esotropia is generated by an increased convergence response for the amount of accommodation (focusing effort). Although refractive error in high AC/A ratio accommodative esotropia has minimal hyperopia, it can also present in patients with a normal or high hyperopia as well as myopia.
A patient with partially accommodative esotropia will show a reduction in the angle of esotropia with glasses, however a residual esotropia in the setting of full hyperopic correction persists.
Epidemiology
Race
No racial predilection exists.
Sex
No sex predilection exists.
Age
Accommodative esodeviations usually present as early as 6 months to 7 years of age with an average onset of 2 ½ years of age. [2]
Prognosis
Permanent vision loss can occur if strabismus and amblyopia are not treated before patients are 4-6 years. Early treatment of amblyopia may result in improved vision, leading to a better prognosis for binocular vision development and a more stable alignment for surgery if required. [3]
With patients aged 4-5 years, one can attempt to reduce the strength of the hyperopic correction to enhance fusional divergence and to maximize visual acuity. If glasses are worn faithfully and fusional patterns are established, many patients with refractive esotropia can maintain straight eyes without wearing glasses by the time they are teenagers.
Studies have demonstrated binocular fusion (peripherally) in approximately 70% of patients with accommodative esotropia. Stereopsis is also more likely if the patient’s esotropia is treated before it becomes constant and they did not require bifocals or surgery. [4, 5]
