good. However, persistent exotropia commonly worsens over time. Base-in prisms, patching, and optical management may be used for such patients. If the deviation progresses, surgical options include re-recession of the lateral rectus muscles, resections of the medial rectus muscles, or injections of botulinum toxin.
Some patients develop monofixational exotropia (a constant exodeviation <8Δ) after treatment of intermittent exotropia. These patients have decreased stereopsis, as occurs in patients with the more common monofixational esotropia (see Chapter 8).
Over time, patients with small-angle esotropias following surgery are less likely to develop recurrent exotropia. However, conversion to monofixation, with subnormal stereopsis, may occur in these patients. For this reason, some ophthalmologists prefer to delay surgery in young children in whom good preoperative visual acuity and stereopsis might be exchanged for a small-angle esotropia and decreased stereopsis postoperatively. However, other ophthalmologists worry that delaying surgery too long could allow permanent suppression to develop and decrease long-term stability following surgical correction.
Convergence Weakness Exotropia
Convergence weakness exotropia is present when the near deviation is greater than the distance deviation. There are 2 main types of convergence weakness exotropia: convergence insufficiency (CI), in which there is usually no distance deviation, and convergence weakness associated with exotropia at both distance and near fixation, but greater at near.
The presentation and management of CI differ from those of other types of exotropia. Patients typically have minimal or no deviation at distance. They are usually older, often teenagers or adults. CI is seen more commonly in patients with Parkinson disease than in age-matched controls. Symptoms of CI include asthenopia, blurred near vision, and diplopia, and they are most noticeable during reading. Evaluation reveals poor near fusional convergence amplitudes and a remote near point of convergence. In rare cases, accommodative spasms may occur if accommodation and convergence are stimulated in an effort to overcome the CI.
Treatment of CI typically involves orthoptic exercises. Base-out prisms can be used to stimulate fusional convergence during reading. Stereograms, “pencil push-ups,” and other near-point exercises are often employed. Also, computer-based convergence training programs are available. If these exercises fail, base-in prism reading glasses may be used. Surgical treatment, usually medial rectus muscle resections, may be indicated in patients whose problems persist despite medical therapy.
The second type of convergence weakness is present when there are manifest deviations at distance and near, but greater at near. Some patients with this type have had previous medial rectus muscle recessions and may show underaction of these muscles. Advancement of the previously recessed medial rectus muscles, with or without recession of the lateral rectus muscles, is commonly used to treat these patients. For patients with convergence weakness who have not had previous surgery, a procedure in which the standard amount of lateral rectus muscle recession and medial rectus resection (see Chapter 14) are reversed may be useful.
Kraft SP, Levin AV, Enzenauer RW. Unilateral surgery for exotropia with convergence weakness. J Ped Ophthalmol Strabismus. 1995;32(3):183–187.
Constant Exotropia
Constant exotropia is encountered most often in older patients with sensory exotropia or patients with long-standing intermittent exotropia that has decompensated.
Surgical treatment of constant exotropia usually consists of either bilateral lateral rectus muscle recessions or unilateral lateral rectus muscle recession combined with medial rectus muscle resection. For patients with very large (>50Δ) deviations, surgery on 3 or 4 muscles is sometimes performed.
Some patients have an enlarged field of peripheral vision because they have large areas of nonoverlapping fields. These patients may notice a field constriction when the eyes are straightened.
Infantile Exotropia
Infantile exotropia is much less common than infantile esotropia. It presents before age 6 months with a large-angle constant deviation (Fig 9-1). Although infants with constant exotropia may be otherwise healthy, they are at increased risk of having associated neurologic impairment or craniofacial disorders. A careful developmental history is important, and referral for neurologic assessment should be considered if there are indications of delay. Patients with constant infantile exotropia are operated on early in life, with outcomes being similar to those for infantile esotropia (see Chapter 8). Early surgery can lead to monofixation with gross binocular vision, but restoration of normal binocular function is rare. Patients may develop dissociated vertical deviations and overelevation in adduction (see Chapter 11).
Figure 9-1 Infantile exotropia. A, This 10-month-old infant with infantile exotropia also shows developmental delay. B, Krimsky testing using 2 base-in prisms to measure the large exotropia. (Reproduced from Wilson ME. Exotropia. Focal Points: Clinical
Modules for Ophthalmologists. San Francisco: American Academy of Ophthalmology; 1995, module 11.)
Sensory Exotropia
Any condition that severely reduces vision in 1 eye—for example, anisometropia, corneal or lens opacities, optic atrophy or hypoplasia, retinal lesions, or amblyopia—can cause sensory exotropia. It