Purpose: To verify the effect of unilateral lateral rectus recession for each millimeter according to the tendon width in intermittent exotropia.
Methods: A total of 37 patients (37 eyes) of 7 to 11 years of age with basic-type intermittent exotropia and a deviation of 16-25 Prism Diopters (PD) were included in this study. Under general anaesthesia, the tendon width of the lateral rectus of the deviating eye near insertion was measured with calipers, prior to dissection of the muscle tendon from the sclera. Patients underwent 6.5-10 mm unilateral lateral rectus recession. The effect of lateral recession for each millimeter was the absolute value of the angle of preoperative deviation plus postoperative deviation on the second day divided by the total amount of recession.
Results: Mean tendon width of the lateral rectus of a deviating eye was 8.3 mm (range: 6.5-9.5). The mean effect per millimeter of unilateral rectus recession in those 37 patient was 2.98+/-0.42 PD (range: 2.4-4.1). The effect of recession was larger in cases in which the tendon width of the lateral rectus was narrower (P=0.000, r=0.72).
Conclusion: The tendon width of the lateral rectus muscle can be a useful indicator to estimate the effect of lateral rectus recession in intermittent exotropia.