Surgically induced incomitance following unilateral versus bilateral medial rectus recessions for esotropia

For small-angle strabismus, unilateral medial rectus recession (UMR) offers many advantages over bilateral procedures (BMR), including a shorter operative time, faster recovery and fewer complications, while preserving the contralateral medial rectus muscle. However, the asymmetric nature of the procedure poses a theoretical risk of induced incomitance in the direction of action of the recessed muscle. This study aims to compare the incidence and nature of induced incomitance following unilateral and bilateral medial rectus recession in the management of non-accommodative esotropia.

Through a retrospective chart review, we identified 43 patients who underwent surgical management for esotropia in the form of UMR (n = 21) or BMR (n = 22). The exclusion criteria included previous strabismus surgery and simultaneous surgery on the oblique muscles. Measurements of deviation in lateral gaze were obtained pre- and post-operatively using the prism cover test (PCT) in nine positions of gaze. Incomitance was defined as a horizontal deviation difference of > 5PD between primary and lateral gaze.

Surgically induced incomitance was observed in 2 patients (9.5%) in the UMR cohort and 2 patients (9.1%) in the BMR cohort (p = 1.00). The mean magnitude of induced incomitance among affected patients was 9 PD in UMR vs. 8 PD in BMR. No statistically significant associations were found between the occurrence of incomitance and age, pre-operative deviation, amount of recession or follow-up duration (p > .05). All patients suffering from post-operative incomitance reported diplopia that resolved over time and did not need further intervention. Higher values of incomitance were associated with a more prolonged period of diplopia.

Our data demonstrates comparably low rates of induced incomitance in the management of esotropia after UMR and BMR, with no significant statistical difference. Our findings support the viability of unilateral recessions for small-to-moderate esotropias.