Intermittent Exotropia: Board Guide
Master intermittent exotropia for NBEO and OKAP: control grading, distance-near patterns, the patch test and management logic.
In intermittent exotropia, what keeps the eyes aligned most of the time?
Intermittent Exotropia in 30 Seconds
Intermittent exotropia is an intermittent manifest exodeviation in which fusion maintains alignment most of the time but periodically breaks down, allowing one eye to drift outward. The deviation is commonly greater at distance than at near, although basic and convergence insufficiency patterns also occur. For NBEO and OKAP, grade control, measure the largest reproducible angle and separate true from pseudo-divergence excess.
What Makes It Intermittent
Fusional convergence holds the deviation in check part of the time. With good control the eyes stay aligned. When control breaks, one eye drifts outward. Fatigue, illness, inattention, bright light and distance fixation commonly expose the tropia. Assess control before dissociating the eyes, since repeated cover testing can artificially worsen it. Good control means the deviation appears only after dissociation and fusion returns quickly. Poor control means spontaneous exotropia or failure to recover alignment.
Distance-Near Patterns
Classification should be based on the largest reproducible deviation after eliminating fusional convergence, typically with prolonged alternate cover testing and, when indicated, 30 minutes of monocular occlusion.
- Basic: distance and near deviations within 10 prism diopters of each other.
- Divergence excess: distance exceeds near by 10 prism diopters or more.
- Convergence insufficiency type: near exceeds distance by 10 prism diopters or more. Do not confuse this subtype with convergence insufficiency as a separate diagnosis.
- Pseudo-divergence excess: the near deviation rises to within 10 prism diopters of distance after 30 minutes of monocular occlusion.
4 Facts Exams Always Ask
- Control grading and evidence of progression, not the prism measurement alone, drive management. Measure the largest reproducible angle rather than accepting the first value obtained.
- Monocular eye closure in bright sunlight is the classic historical clue.
- Amblyopia is uncommon in alternating intermittent exotropia because both eyes take turns fixing and neither is chronically suppressed.
- The board sequence: measure distance and near, patch one eye for 30 minutes, then remeasure near. If the near deviation rises toward the distance value, the pattern is pseudo-divergence excess. If distance still exceeds near by 10 prism diopters or more, add a plus 3.00 D lens at near. An increase points to true divergence excess with a high AC/A ratio.
The Classic Trap
Do not decide management from the prism diopter measurement alone. A large angle with excellent control and preserved stereoacuity may warrant observation, while a smaller angle with deteriorating control may warrant surgery. A second trap is calling a distance-greater deviation true divergence excess before the patch test, since pseudo-divergence excess changes surgical planning. Loss of distance stereoacuity is a more sensitive marker of deteriorating control than near stereoacuity, which often stays normal until later in the disease.
Clinical Pearl
Non-surgical management comes first: full refractive correction, especially in myopia where clearer vision aids fusion, overminus lenses in selected children and part-time patching in selected young children. Vision therapy is well established for convergence insufficiency but has a limited role in routine intermittent exotropia. Consider surgery when the manifest phase becomes more frequent, recovery after dissociation worsens, the angle increases, distance stereoacuity declines or the patient develops diplopia or asthenopia. Age alone does not determine surgical timing.
Checkpoint 1
An intermittent exotropia measures 30 prism diopters at near and 16 prism diopters at distance. Which pattern does this represent?
Checkpoint 2
Which measure is the more sensitive indicator of deteriorating control in intermittent exotropia?
A 6-year-old is noted to drift one eye outward only at the end of the day when tired. On cover testing the deviation recovers immediately and fusion returns. Distance stereoacuity is normal. There is no diplopia or asthenopia. The deviation measures 18 prism diopters at distance and 14 prism diopters at near.
What is the most appropriate management?
Sources & Reviewer Info
Diagram created with AI image generation, clinically reviewed for accuracy.
References
- American Academy of Ophthalmology. Basic and Clinical Science Course, Section 6: Pediatric Ophthalmology and Strabismus.
- American Association for Pediatric Ophthalmology and Strabismus. "Intermittent Exotropia."
- American Academy of Ophthalmology EyeWiki. "Intermittent Exotropia."
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