Strabismus is a misalignment of the eyes such that both eyes are not directed simultaneously at the same object. Esotropia is a type of strabismus characterized by an inward deviation of one eye relative to the other eye. The accommodative convergence/accommodation (AC/A) 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). Esotropia with high AC/A ratio (also termed nonrefractive accommodative esotropia) combines a high AC/A ratio with low hyperopia or even myopia. Amblyopia (reduced visual acuity due to an abnormal visual experience early in life) frequently develops if the condition remains untreated.[1]
No racial predilection exists for esotropia with high AC/A ratio.
No sex predilection exists for esotropia with high AC/A ratio.
Esotropia with high AC/A ratio presents by the age of 2 years.
Parents of the patient may notice an inward or upward deviation of one eye relative to the other eye. The patient may see either a single blurred image or a double image in which one image is clear and one image is blurred.
The age of onset of strabismus should be noted. Family history of strabismus or related diseases is common.
Carefully examine visual acuity in a manner appropriate for the patient's age. For patients younger than 1 year, visual acuity is measured by objective means.[2] For patients aged 1-3 years, subjective methods, such as Allen cards, are used in addition to objective methods. For patients aged 3-5 years, subjective methods, such as Allen cards, tumbling Es, or the letter chart, can be used. For patients older than 5 years, the Snellen alphabet chart almost always can be used. The patient usually will have hyperopia in the range of +3.00 to +10.00 diopters.
Determine stereo acuity using polarized glasses and Titmus test or Randot stereograms.
Check extraocular movements to ensure that eye movements are full.
Measure or estimate angle of deviation. This measurement can be performed most easily by evaluating the centration of the corneal light reflex in each eye, while the patient fixes on objects at distance or near. In some cases, it is possible to perform the alternate cover test. The examiner asks the patient to fix on an object. By alternately covering and uncovering each eye, the examiner can detect a shift in the eye's position with refixation. In esotropia, the uncovered eye turns out to fixate. The angle of deviation is greater with near fixation than at distance and usually is 20-40 prism diopters.
Measure AC/A ratio. Patients with nonrefractive accommodative esotropia have a high AC/A ratio, which results in a deviation measured at near that is significantly greater than that at distance. In contrast, the AC/A ratio is normal (ie, distance and near measurements are the same) in pure accommodative esotropia.
Perform complete eye examination. Examine the anterior segment to assess the cornea, anterior chamber, and lens. Examine the fundus with both direct and indirect ophthalmoscopes. Note the appearance of the macula and the optic nerve.
Perform cycloplegic refraction on all children by using the retinoscope and loose lenses. Cycloplegia is achieved with Mydriacyl 1% if the patient is younger than 1 year; it is achieved with Cyclogyl 1% if the patient is older than 1 year.
Treatment of nonrefractive accommodative esotropia consists of full correction for the distance refractive error and bifocals for near vision to suspend the accommodative drive and to lessen accommodative convergence.
Bifocal power should be +2.50 to +3.00 diopters, and bifocals should be placed such that the upper boarder of the bifocal segment bisects the pupil. Miotics, which lower the AC/A ratio, are successful in some patients. In cases of amblyopia, early treatment of patching the normal (unaffected) eye is the mainstay of treatment.[3, 4]
Surgery may be required if the esodeviation becomes refractory to optical treatment. Surgery often is needed when optical treatment is delayed.[5] Surgical treatment typically entails recession or weakening of the inward-pulling medial rectus muscle in each eye. Surgery is performed for the nonaccommodative component only. The operation is not intended to discontinue use of glasses.
Patients who are treated for amblyopia should be seen at 1- to 4-month intervals depending on their age. Stable patients are typically seen every 6 months. Cycloplegic refraction is repeated at least annually and any time esotropia worsens.
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 development of binocular vision and a more stable alignment if surgery is required. Most patients can be weaned from their bifocals by the time they are teenagers.
Managing nonrefractive accommodative esotropia can be difficult and frustrating because patients may vary in their ability to fuse despite faithful wearing of glasses.