Adjustment sensitivity of horizontal rectus muscles in adjustable strabismus surgery

A "marking suture" was used in 12 consecutive cases of adjustable strabismus surgery to determine the relationship between ocular alignment and the amount of horizontal muscle adjustment. The average change in ocular alignment was 2.55 prism diopters for each millimeter of muscle adjustment. Regression analysis revealed the relationship to be linear over the range of adjustments studied. The sensitivity of adjustment was the same whether the adjusted muscle was advanced or further recessed and whether the adjusted muscle was the medial rectus or the lateral rectus. No relationship was found between the distance of a recessed muscle from its normal insertion and the subsequent adjustment sensitivity of that muscle. This information, when used clinically in conjunction with a marking suture, can facilitate the adjustment phase of adjustable strabismus surgery.