Is surgical intervention on one or two extraocular eye muscles indicated for a patient with constant large-angle exotropia and double vision?

Surgical Intervention is Clearly Indicated

Yes, surgical intervention on extraocular eye muscles is definitively indicated for this 17-year-old female with constant large-angle exotropia (45 prism diopters) and constant diplopia. 1

Primary Indication for Surgery

This patient meets multiple clear surgical criteria according to the American Academy of Ophthalmology guidelines:

• Constant exotropia is an absolute indication for surgical intervention, as the deviation is no longer intermittent and represents complete loss of fusional control 1
• Constant diplopia indicates symptomatic deterioration and loss of binocular fusion, which threatens quality of life and requires surgical correction 2
• Large-angle deviation of 45 prism diopters represents a substantial exodeviation that is "so large as to be unacceptable" per guideline criteria 2
• The 2-year progressive worsening demonstrates failed conservative management and deteriorating control 2

Surgical Approach: Unilateral Two-Muscle Surgery Preferred

For this patient, unilateral surgery on the left eye (the eye with poorer vision) is the recommended approach:

• When poor vision is present in one eye, unilateral surgery on that eye is typically preferred (lateral rectus recession + medial rectus resection) 1
• The left eye has worse vision (20/40 vs 20/33) and more astigmatism, making it the appropriate surgical target 1
• Both unilateral two-muscle surgery and bilateral surgery produce equivalent outcomes, with no significant difference at 6 months and 3 years postoperatively in a large clinical trial of 197 children 1, 2

Why Not Bilateral Surgery in This Case

While bilateral lateral rectus recession is an acceptable alternative, unilateral surgery is more appropriate here because:

• The patient has unequal vision between eyes, which specifically favors unilateral surgery on the poorer-seeing eye 1
• The deviation is equal at distance and near (45 prism diopters at both), which does not specifically favor bilateral surgery 1
• No A or V pattern is mentioned, which would otherwise favor bilateral surgery 1

Critical Preoperative Considerations

Before proceeding to surgery, ensure the following assessments are completed:

• Measure the deviation at near, distance, and remote distance with best optical correction to confirm the full magnitude 1, 2
• Perform a 30-minute monocular occlusion (patch test) to elicit the maximum deviation 1, 2
• Assess AC/A ratio using −2.00 D lenses over distance correction; if the distance angle decreases significantly, a high AC/A ratio may warrant caution due to risk of consecutive esotropia with diplopia at near 1
• Correct the astigmatism fully before final surgical measurements, as refractive changes can alter the measured deviation 1

Important Surgical Pitfalls to Avoid

Be aware of these specific complications:

• Postoperative consecutive esotropia can occur and cause persistent diplopia, particularly problematic since this patient already has constant diplopia preoperatively 1, 2
• Delaying surgery in patients with constant exotropia and diplopia leads to progressive deterioration and potential permanent loss of binocular function 2
• Recurrence is common over time: approximately 80% have good alignment at 6 months, but long-term results show frequent recurrence 1, 2
• If consecutive esotropia persists for several weeks postoperatively, temporary membrane prisms should be used and slowly reduced; if unsuccessful, additional surgery may be required 1

Expected Outcomes

Realistic expectations for this patient:

• Success rate for large-angle constant exotropia is lower than for intermittent exotropia 3
• For very large-angle exotropia (this patient's 45 prism diopters qualifies), success rates of 80-83% for primary gaze alignment are achievable 4, 3
• Normal binocular function is rarely achieved in constant exotropia, even with surgery 1
• The patient's age (17 years) is favorable, as she can cooperate with postoperative management 1