Acquired Exotropia Clinical Presentation
- Author: Neepa Thacker, MBBS, MS, DNB, FRCS; Chief Editor: Hampton Roy, Sr, MD more...
See the list below:
- Clinical presentation
- Patients may experience asthenopia (eyestrain) during visual tasks, especially after prolonged near work. A common complaint is that a patient loses his or her place on a line while reading and repeatedly restarts on the same line.
- Diplopia that is horizontal and crossed (ie, the right eye sees the image on the left, and the left eye sees the image on the right) may develop in some patients.
- Some patients are subjectively aware of when the divergence of their eyes occurs, and they are able to volitionally restore binocularity.
- Some patients may complain that objects appear smaller and closer because they use accommodative convergence to control the exodeviation.
- Children characteristically close one eye in bright light. This action may precede the actual divergence of the eyes, or the parents may notice this phenomenon, which becomes the presenting complaint. Although various theories have been proposed to explain this phenomenon (eg, glare hinders fusion and causes its disruption), it remains incompletely understood.
- Some attentive patients may notice an increase in the temporal visual field of the affected eye, called panoramic viewing.
- Classification systems
- Duane classification
- If the deviation is greater at distance than at near, it is called the divergence excess type of exotropia.
- If the deviation is greater at near than at distance, it is called the convergence insufficiency type of exotropia.
- If little (< 10 prism diopters [PD]) or no difference exists between distance and near deviation, it is called the basic type of exotropia.
- Burian classification
- The divergence excess type of exotropia occurs when the deviation is greater at distance than at near (same as Duane classification). Burian divided it into 2 types: simulated divergence excess and true divergence excess. The simulated divergence excess type of intermittent exotropia demonstrates an increase in the near deviation after monocular occlusion or with +3.00 diopter (D) lenses placed in front of the habitual (if any) spectacle or contact lens prescription. If no increase occurs in the near deviation with either test, a true divergence excess type of intermittent exotropia is present.
- The basic type of exotropia occurs when little or no difference exists between distance and near deviation (same as Duane classification).
- The convergence insufficiency type of exotropia occurs if the deviation is greater at near than at distance (same as Duane classification).
- Kushner classification
- This classification system takes into account the effect of monocular occlusion, the use of either -2.00 D lenses or +3.00 D lenses, and the accommodation convergence-accommodation (AC/A) ratio.
- The Kushner classification of intermittent exotropia is depicted in the image below.
- Duane classification
A complete ophthalmic examination and an ocular motility examination should be performed in each patient.
Specific parts of the examination are outlined below, followed by physical findings of the different types of acquired exotropia.
- Measurement of the deviation
- Distance deviation is measured at 6 meters with an accommodative target; target size is 20/70 or smaller.
- Far distance deviation is measured when the patient looks out of a window or at any target 50-100 feet away. This method may help obtain the full exotropic angle, which may increase from 10 PD to 30 PD when compared to the distance deviation measured at 6 meters.
- Near deviation is measured at 33 centimeters with an accommodative target.
- Deviation is measured after monocular occlusion to disrupt fusional convergence. Distance and near measurements are taken after patching either eye for at least 30-45 minutes.
- Deviation is measured after using either +3.00 D lenses (near deviation) or –2.00 D lenses (distance deviation) to disrupt the accommodative convergence. The deviation with +3.00 D lenses should always be measured after the monocular occlusion test to avoid an erroneous measurement of a high AC/A ratio.
- Assessment of the control of the deviation
- This testing is important to obtain a baseline assessment and to monitor deterioration and progression of the intermittent exotropia.
- Subjective methods
- In home control, parents assess the deviation. The assessment of deviation is categorized as follows: excellent control, where deviation occurs rarely or only at distance when tired, fatigued, or inattentive; good control, where deviation occurs less than 5 times a day and only at distance; fair control, where deviation occurs more than 5 times a day and only at distance; or poor control, where deviation occurs frequently at distance and near.
- In office control, ophthalmologists assess the deviation in a clinical setting. The assessment of deviation is categorized as follows: good control, where the patient breaks down only after cover testing and resumes fixation without a blink; fair control, where the patient breaks down after cover testing and blinks to refixate; or poor control, where the patient breaks down without any form of fusion disruption.
- Objective methods
- Distance stereoacuity provides an objective measure of the control of the deviation and the deterioration of fusion.
- Near stereoacuity does not correlate well with the degree of control of the distance deviation.
- Amblyopia does not occur as frequently in patients with intermittent exotropia as in patients with esotropia. This type of amblyopia is usually nonstrabismic and frequently anisometropic.
- Assessment of refractive error is an important part of the examination because unequal visual clarity could hinder binocular fusion and lead to the progressive loss of control of the exotropia. Cases of exotropia resolving after the optical correction of a high hyperopic refractive error have been reported.
- Sensory changes
- Suppression may be noted. Alternate suppression with temporal scotomas (which tend to split fixation) has been demonstrated in 52% of patients with intermittent exotropia.
- Retinal correspondence is determined.
- Distance and near stereoacuity is assessed.
- Lateral incomitances
- The size of the deviation differs in the primary position and in the lateral gaze positions.
- Horizontal incomitance has been reported in 5-60% of patients with exotropia.
- Recognizing lateral incomitance is important since an alteration of the surgical strategy to avoid diplopia in side gaze postoperatively may be required.
- Vertical incomitances
- The incidence of A- and V-pattern strabismus and oblique muscle dysfunction is lower in exotropia than in other types of strabismus.
- The most common pattern associated with exotropia is V-pattern strabismus.
- X-pattern exotropia can occur secondary to the overaction of the inferior and superior oblique muscles.
- Convergence: When the deviation is greater at near than at distance, convergence insufficiency is possible.
- Sensory exotropia is a condition of unilateral divergence as a sequela to loss of vision or long-standing poor vision in one eye.
- Sensory exotropia can occur because of visual loss at any age. In younger children, the incidence of esotropia or exotropia occurring in the nonseeing eye is about equal. In adults, the tendency is toward exotropia.
- Sensory exotropia accounts for 20-25% of all causes of acquired exotropias.
- The deviation angles are characteristically large. An eye with long-standing sensory exotropia often develops any of the several mechanical and innervational abnormalities, especially if the angle is large. These abnormalities include tight lateral rectus muscle syndrome with limited adduction, secondary pseudo–oblique muscle overaction, and shortening and tightening of the Tenon capsule and the conjunctiva over the lateral rectus muscle.
- Superior oblique overreactions with A-pattern strabismus are more common than V-pattern strabismus.
- On examination, the deviation needs to be measured with the Krimsky test or the light reflex-prism test if the visual acuity in the exotropic eye is poor.
- Exotropia can develop if both eyes have a significant visual field loss. Exotropia may occur with either bilateral homonymous field defects or heteronymous defects (eg, bitemporal field defects). This condition is uncommon.
- Exotropia with bilateral homonymous visual field defects
- Acquired neurologic disorders may produce bilateral homonymous field defects. Some patients may develop exodeviations, mostly exophorias or small intermittent exotropias.
- Characteristically, these patients have normal retinal correspondence and good fusional ability. They do not have significant visual difficulties. Patients rarely complain of diplopia.
- Whether the exotropia that develops is a true compensatory phenomenon or a coincidental finding is unclear. The exotropia may be helpful by allowing enlargement of the total visual field.
- Exotropia with bitemporal visual field defects
- Bitemporal hemianopia, which may occur with lesions (eg, pituitary tumors, aneurysms near the optic chiasma), is rarely associated with exotropia.
- Unlike a homonymous field defect, a bitemporal defect always interferes with fusion, and, in cases where strabismus develops, a significant field loss, including central vision, occurs in both eyes.
- These patients are usually disturbed by the symptoms of disordered binocular vision. Because of retinal sliding, the patients have a subjective sensation of an elongated target or a duplication of some features of a target. Loss of fixation beyond the fixation target may occur. All of these phenomena make routine visuomotor tasks difficult.
- Exotropia with bilateral homonymous visual field defects
- Consecutive exotropia, also called secondary exotropia, is the type of exodeviation that occurs after surgical overcorrection of an esodeviation.
Hereditary does play a role, but the genetics of this disorder are multifactorial. Exodeviations tend to occur earlier and to be larger in successive generations.
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