Is surgical intervention on one or two extraocular muscles indicated for a patient with poorly controlled intermittent exotropia (XT) of 50 prism diopters, who has not improved with patching and is now experiencing diplopia?

Surgical Intervention is Indicated for This Patient

Yes, surgery on extraocular muscles is clearly indicated for this patient with poorly controlled intermittent exotropia of 50 prism diopters who has failed conservative management and is now experiencing diplopia with suppression. 1

Indications for Surgery Met

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

• Large deviation magnitude: 50 prism diopters is a substantial exodeviation that is "so large as to be unacceptable" 1
• Failed conservative treatment: 3 months of patching therapy showed no improvement 1
• Symptomatic deterioration: New onset diplopia indicates loss of fusional control 1
• Developing suppression: The patient is starting to suppress the right eye, which threatens binocular vision and quality of life 1

The presence of diplopia in intermittent exotropia is particularly concerning, as these patients typically do not experience diplopia due to intact fusion mechanisms. When diplopia develops, it signals deteriorating fusional control requiring surgical correction. 1

Surgical Options: One vs Two Muscles

Both unilateral two-muscle surgery and bilateral two-muscle surgery are appropriate options, with equivalent outcomes. 1

Surgical Approaches:

Bilateral lateral rectus recession (operating on 2 muscles, one in each eye):

• Preferred by some surgeons for large deviations 1
• Recession amounts based on the distance deviation 1

Unilateral recession-resection (operating on 2 muscles in one eye):

• Lateral rectus recession and medial rectus resection/strengthening 1
• A large clinical trial of 197 children showed no significant difference in outcomes between bilateral and unilateral approaches at 6 months and 3 years postoperatively 1
• May be preferred when poor vision is present in one eye 1

Key Surgical Considerations:

• Preoperative measurements: Obtain measurements at near, distance, and remote distance with best optical correction 1
• Patch test: Perform 30 minutes of monocular occlusion to elicit the full deviation 1
• AC/A ratio assessment: If distance angle exceeds near angle by ≥10 prism diopters, place -2.00 D lenses over correction to assess for high AC/A ratio 1
• Refractive correction: The patient has minimal hyperopia (+0.50 -0.75 x 15 OD, plano OS), which should not significantly influence surgical planning 1

Clinical Pitfalls to Avoid

Do not delay surgery in this patient despite the intermittent nature of the exotropia. The development of diplopia and suppression indicates progressive deterioration that threatens permanent loss of binocular function. 1

Beware of postoperative overcorrection: Consecutive esotropia can occur and may cause diplopia, particularly problematic in patients who already experienced diplopia preoperatively. 1 However, some studies suggest early overcorrection may improve long-term alignment, though outcomes are variable. 1

Monitor for recurrence: Approximately 80% of patients have good alignment at 6 months, but long-term results show recurrence is common over time. 1 Plan for long-term follow-up.

Specific Recommendation

For this patient with 50 prism diopters of exotropia, either bilateral lateral rectus recession OR unilateral lateral rectus recession with medial rectus resection is appropriate, with the choice based on:

• Presence of fixation preference (if suppressing right eye consistently, consider unilateral surgery on that eye) 1
• Presence of A or V pattern (bilateral surgery preferred if present) 1
• Surgeon experience and preference 1

The critical point is that surgery should proceed promptly given the symptomatic deterioration and threat to binocular vision, not whether one versus two eyes are operated upon. 1