Question of the Week

A 5-year-old child underwent bimedial rectus recessions of 6.0 mm each for a 45-prism-diopter esotropia. Initially, the eyes were well aligned. Six months later, the parents report that the child appears to be “looking outwards,” especially when focusing on distant objects. On examination, you note a 20-prism-diopter exotropia at distance and 10-prism-diopter exotropia at near. Visual acuity is equal in both eyes and there is no amblyopia. Versions show full motility.

Which of the following is the most likely explanation for this new ocular misalignment?

A. Progressive lateral rectus tightness due to postoperative scarring
B. Consecutive exotropia resulting from large medial rectus recessions
C. Unmasking of a previously latent exophoria unrelated to surgery
D. Symmetric lateral rectus insertion slippage
E. Development of inferior oblique overaction following medial rectus recession

Answer

Correct Answer: B

Consecutive exotropia can occur after large bimedial rectus recessions, especially when the preoperative angle was large or if accommodative tone decreases over time. The medial rectus muscles are now weakened relative to the lateral rectus muscles, resulting in outward drift.

Key points:

Large medial rectus recessions (>5.5 mm) may weaken convergence and lead to exotropic drift over time.
More common in large-angle infantile or early-onset esotropia and patients with high AC/A (accommodative convergence/accommodation) ratio once they lose accommodation.
Early signs include exotropia at distance, as distance fixation uses less accommodative convergence.