Consecutive exotropia: why does it happen, and can medial rectus advancement correct it?

PURPOSE

To investigate whether consecutive exotropia following medial rectus muscle recession is associated with muscle slippage and to assess the effectiveness of treating the condition with medial rectus advancement.

METHODS

The records of patients with consecutive exotropia after medial rectus recession were reviewed to determine medial rectus muscle insertion location at the time of advancement surgery. Measurements before and after medial rectus advancement were compared. Success was defined as alignment within 10(Δ) of orthotropia. The dose effect of medial rectus advancement was determined by nonlinear regression.

RESULTS

A total of 20 patients were included. The mean age (± standard deviation) at time of surgery was 19 ± 19 years (range, 1.1-65.4). The mean preoperative exotropia was 28(Δ) ± 16(Δ) (range, 12(Δ)-60(Δ)). Medial rectus slippage of 2.5 ± 1.7 mm (range, 1.0-5.0 mm) was found in 14 patients (36%) who had previously undergone medial rectus recession. Surgery corrected about 4(Δ) of exotropia per mm total medial rectus advancement. Although 95% of patients were aligned successfully immediately after surgery, averaging 2(Δ) ± 4(Δ) esotropia, there was significant late exodrift, averaging 17(Δ) at final follow-up. At final follow-up, 1.6 ± 1.8 (range, 0.10-6.2) years after surgery, 50% of patients maintained alignment within 10(Δ) of orthotropia (mean, 3(Δ) ± 4(Δ) exotropia); the rest experienced recurrent exotropia of 25(Δ) ± 8(Δ).

CONCLUSIONS

Medial rectus slippage is common in consecutive exotropia. Medial rectus advancement effectively treated consecutive exotropia, whether or not there was muscle slippage. It is however, associated with late exodrift; hence patients should be warned about potential for further XT recurrence.