Accommodative Esotropia

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]

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.

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]

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]

Parents of the patient may notice an inward or upward deviation of one eye relative to the other eye especially when the child is focusing at near or is tired. In younger children, they may rub their eyes, squint, and complain of headaches or diplopia.{ref13-INVALID REFERENCE} The patient may see either a single blurred image or a double image in which one image is clear and one image is blurred. Family history of strabismus or related diseases is common. The age of onset of strabismus should be noted.

Carefully examine visual acuity in a manner appropriate for the patient's age. For patients younger than 2 years of age, visual acuity is measured by subjective means. For older patients, objective methods, such as Allen or LEA pictures, HOTV matching, tumbling E, and Snellen letter chart, can be used.

Determine stereo acuity using polarized glasses and Titmus test or Randot stereogram.

Check extraocular movements to ensure that the eye movements are full. Versions and ductions may be normal or include over elevation in adduction consistent with inferior oblique overaction.

Measure or estimate the angle of deviation. The easiest method to evaluate ocular alignment is observation of the centration of the corneal light reflex in each eye, while the patient fixes on objects at distance or near (Hirschberg method) and neutralize this light reflex with prism (Krimsky method). In some cases, it is possible to perform the alternate prism cover test. The patient is first asked to fixate on an object. By alternately covering and uncovering each eye while the patient maintains fixation, the examiner can detect a shift in the eye's position with refixation and measure the objective amount of this misalignment with prism. In esotropia, as an eye is uncovered, it turns out to fixate. In true accommodative esotropia, the angle of deviation is the same when measured at distance and near fixation and usually is 20-40 prism diopters (PD).

Measure AC/A ratio. If this ratio is high, then the deviation measured at near will be significantly greater than that at distance, usually with a threshold of 10 PD used to signify a difference. In pure accommodative esotropia, the AC/A ratio should be normal; distance and near measurements should be similar.

Perform a 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 or the phoropter to neutralize the retinoscopic light reflex. The patient usually will have hyperopia in the range of +3.00 to +10.00 diopters, with an average of +4.00 diopters in refractive accommodative esotropia and +2.25 diopters in high AC/A accommodative esotropia.

As previously mentioned, accommodative esotropia is frequently associated with amblyopia. Many children experience rapid suppression as their visual system tries to avoid diplopia and confusion. It is extremely important to catch these findings early in infants/children due to their shorter critical period and plasticity of their cells in the primary visual cortex in response to visual stimulation. Therefore, timely detection and intervention is needed to promote use of the amblyopic eye (ie with cataract removal, refractive correction, occlusion therapy) before visual defects become permanent.{ref 12}

Laboratory studies are traditionally unnecessary in the evaluation and work up of accommodative esotropia. However, if there is concern for Myasthenia gravis or thyroid eye disease, appropriate studies may be undertaken.

Typically, imaging is not required to aid in the diagnosis of traditional accommodative esotropia. However, sometimes patients present with an acute onset of esodeviations after illness or minor trauma, which is unmasked accommodative esotropia. These patients need neuroimaging (MRI, CT, etc.) to rule out other pathology as the etiology of an acquired esotropia. Additionally, if esotropia is identified in conjunction with an abduction deficit, evaluation should proceed with neuroimaging.[6] The patient’s history and clinical exam should be taken into account when deciding to obtain neuroimaging. Although rare, intracranial tumors and other CNS tumors can result in a life-threatening outcome if an appropriate work up is not performed.  

Refer to “Surgical Care” section.

For refractive accommodative esotropia, treatment is determined by cycloplegia. Prescription of the full amount of hyperopic correction provides adequate treatment for refractive (accommodative) esotropia in 75% of cases.[7, 8]

Patients with a high AC/A ratio accommodative esotropia can be given bifocals to reduce the need to accommodate for near fixation. The goal of bifocals is to restore normal fusion and stereopsis at both distance and near fixation.

Anticholinesterase miotic agents may also be used in children who lack cooperation with glasses wear. Echothiopate iodide 0.125% reduces the accommodative effort by acting as a parasympathomimetic on the iris sphincter and ciliary muscle. It can be given for 2 weeks and then slowly tapered to normalize the AC/A ratio {ref13-INVALID REFERENCE}. However, anticholinesterase drops or ointments are not as effective as glasses. Side effects of anticholinesterase miotic agents may also include retinal detachment, iris cysts, lens opacities, stinging, burning, and lacrimation.

In cases of concurrent amblyopia, early treatment with penalization therapy, such as with patching or atropine penalization of the normal eye, is the mainstay of treatment. This may be undertaken with the start of glasses or afterwards if amblyopia persists despite glasses wear. The choice and order of this treatment is oftentimes dependent on age and cooperation with acuity testing. If surgical treatment is needed, patients can be trialed with prism adaptation prior to surgery. Prism adaptation uses a base-out prism to manage residual esotropia after hyperopic correction.

Surgery may be required if the esodeviation progresses to partially accommodative esotropia, with residual misalignment of greater than 8-10 PD despite correction with full cycloplegic refraction. This amount of misalignment prevents binocular development. Surgery often is needed when optical treatment is delayed.[9]

Surgical treatment typically entails recession or weakening of the inward-pulling medial rectus muscle in each eye. In cases involving amblyopia, surgery can be limited to only the amblyopic eye by performing a recession of the medial rectus and a resection or strengthening of the ipsilateral lateral rectus, so as to put all risk of surgery on the ‘weak’ eye. While surgery is performed for the nonaccommodative component only, the operation is not intended to discontinue use of glasses. However, surgery may allow patients to reduce hyperopic correction and discontinue wear of bifocals in the setting of a preoperatively high AC/A ratio.

The greatest risk of untreated accommodative esotropia is the development of amblyopia and loss of binocular visual development. This risk can be augmented by delay in treatment.

With surgery, there is a risk of overcorrection (< 10%) with development of consecutive exotropia, or undercorrection with persistence of residual esotropia. Additionally, surgical risks include infection, both periocular and endophthalmitis, as well as scleral perforation with associated retinal tear and detachment. More recently, there has been a lower risk of scleral perforation due to surgical technique preference with spatuled needles on the suture to reattach the muscle to the globe.{ref13-INVALID REFERENCE}

For both refractive accommodative esotropia and high AC/A ratio accommodative esotropia, cycloplegic refraction should be repeated as hyperopia tends to increase until 5-7 years of age before plateauing. Follow up should be done to monitor for amblyopia and visual development.

There are no medications for this condition.

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 aged 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.