Vertical Rectus Surgery for Knapp Class II Superior Oblique Muscle Paresis

Abstract

In the first annual Scobee Lecture, Knapp presented a classification and treatment schema for superior oblique muscle palsy that has become a classic in the field of strabismus.¹ Though subsequent advances in our understanding of superior oblique tendon anatomy^2-5 and the popularization of adjustable sutures^6,7 have made some of his treatment recommendations outdated, the underlying concepts behind his recommendations are quite useful. Specifically, Knapp recommended that the magnitude of the deviation determine how many muscles should be operated on, and the incomitance pattern should determine which muscles should have surgery. He chose to operate on muscles that would have the greatest effect in the field of gaze with greatest vertical misalignment and that also address any torsional abnormality. Subsequent authors have incorporated these principles into newer schemas for treating superior oblique muscle paresis, though they deviated from Knapp's recommendations.^8-12