The Effect of Horizontal Rectus Muscle Surgery on Distance-Near Incomitance

To determine the effect of horizontal rectus muscle surgery on distance-near incomitance.

Prospective, comparative, interventional case series.

Prospective evaluation of patients >7 years old who had medial or lateral rectus muscle surgery at the University of Arkansas Medical Center or Arkansas Children's Hospital between December 2009 and January 2012. Prism and alternate cover testing was performed at distance (6 m) and near (0.3 m) fixation after >1 hour of monocular occlusion at preoperative and postoperative examinations within 1 week, and closest to 1 year after surgery. The change in distance-near incomitance was calculated. Patients with extraocular muscle fibrosis or paralysis were excluded.

Forty-five patients met inclusion criteria. Twenty-five patients had medial rectus muscle surgery, and 20 patients had lateral rectus muscle surgery. Postoperative examinations showed a change in distance-near incomitance ≤10 prism diopters (PD) in 42 of 44 patients evaluated within 1 week after surgery and in all 28 patients evaluated 6-24 months after surgery. Horizontal rectus muscle surgery did not induce a clinically significant change in distance-near incomitance (±2 PD equivalence, TOST confidence interval, -1.8 +1.6 PD, P value = 0.014). Contrary to traditional teaching, medial rectus muscle surgery was not more likely to induce a greater effect at near fixation (P = 0.80) and lateral rectus muscle surgery was not more likely to induce a greater effect at distance fixation (P > 0.99).

Horizontal rectus muscle surgery does not induce a clinically significant effect on distance-near incomitance. Contrary to traditional teaching, medial rectus muscle surgery does not induce a greater effect on ocular alignment at near fixation and lateral rectus muscle surgery does not induce a greater effect on ocular alignment at distance fixation. It is not necessary to consider distance-near incomitance when choosing between medial rectus and lateral rectus muscle surgery.