[Induced Incomitance of one Muscle Strabismus Surgery in Comparison to Unilateral Recess-Resect Procedures]

Surgical correction of intermediate squint angles may be performed on one muscle alone or as a combined unilateral recess-resect procedure. No larger case series has yet systematically measured the amount of induced incomitance that could potentially lead to visual disturbances.

31 patients with strabismus and binocular vision (phoria or intermittent strabismus) were operated on one extraocular eye muscle; 30 patients underwent a unilateral recess-resect procedure. Preoperatively and three months postoperatively, we measured the latent angle of squint on a tangent screen over the horizontal 60° in 10° increments and then calculated the amount of induced incomitance.

After one muscle surgery, the induced incomitance was 1.7° over a 20° gaze range, 3.2° over a 40° gaze range and 3.8° over a 60° gaze range. For recess-resect procedures, the induced incomitance was 1.4°, 2.6° and 3.4°, respectively. A significant correlation between the surgical dose and the induced incomitance was only seen in one muscle surgery for the 40° and 60° gaze range, but not for the 20° gaze range. A subgroup analysis of patients with an identical surgical dose in one and two muscle procedures (6-8 mm) found greater induced incomitance in one muscle procedures, but only for the 40° and 60° gaze range (p = 0.02). Double vision in any gaze direction was reported by 16 % of patients after one muscle surgery and 10 % of patients after unilateral recess-resect surgery (p > 0.05).

One muscle surgery is a viable option in small and intermediate angles of squint. The induced incomitance is rather small and does not lead to significant visual disturbances in the central gaze range.