CASE 13: Divergence excess intermittent exotropia
A The eyes are aligned at near.
B After dissociation with the cover test the eyes are 40 prism diopters exotropic and remain so until the child blinks or is reminded this her eye is “out.”
Over the past 2 years, this 4-year-old girl has been noted by her family to have an eye that wanders out when she is tired and when she is looking in the distance. Also, she closes her left eye almost constantly in bright sunlight. The child has been otherwise healthy and is doing well in preschool.
Visual acuity with correction is 20/25 in each eye. Retinoscopy after 1% Cyclogyl is OD +.50, OS +.75. This patient fused 7/9 stereo dots (60 seconds), and her eyes were aligned throughout the early part of the examination. Cover testing revealed 40 prism diopters of intermittent exotropia at distance.
Recovery is fairly brisk, but the left eye does remain exodeviated through a blink and remains exodeviated until the patient changes fixation, usually to near, or her attention is called to the fact that the eye is out.
She experiences no diplopia during this manifest phase. At near, prism and cover test measures 15 prism diopters of intermittent exotropia. Near point of convergence is to the nose. The remainder of the eye examination is completely normal. After wearing a patch over the left eye for 1 hour, near cover testing was repeated without allowing any binocular experience, and the near deviation remained 15 prism diopters intermittent exotropia.
Divergence excess intermittent exotropia.
Bilateral lateral rectus recessing 7.0 mm.
This girl has a fairly classic intermittent exotropia, which is classified as a divergence excess intermittent exotropia because the distance deviation is persistently larger than the near. If, after occlusion of one eye for 1 hour cover testing at near carried out without allowing the patient to become binocular had resulted in a near deviation increasing to become equal or nearly equal to the distance deviation, this could be called a pseudo divergence excess intermittent exotropia. If the distance and near deviation had been equal from the outset, basic exotropia would be the diagnosis. Most patients with intermittent exotropia do well with surgery. However, patients with divergence excess intermittent exotropia may have esotropia at near postoperatively, producing bothersome diplopia and requiring base-out prism. Such treatment may be prolonged for a few weeks or months. In a few cases it has been necessary to recess one or both medial recti in older symptomatic patients. This in turn could cause a return of the distance exodeviation. This response is rare. The amount of surgery is dependent on the angle of deviation. A smaller angle of exodeviation requires a smaller amount of surgery and vice versa, but the timing of intermittent exotropia surgery is done on the basis of how often the eye is deviated, not by how far the eye is out.