Measured graduated recession of the superior oblique muscle.

Six patients underwent bilateral superior oblique recession for A-pattern strabismus with overacting superior obliques. The established technique was modified to permit the entire procedure to be carried out through a single nasal fornix incision. The amount of recession was graduated and measured both directly from the point of the original incision anteriorly and indirectly from the nasal of the corner of the superior rectus insertion based on anatomical measurements. A good correlation was found between the amount (measured directly) of recession performed and reduction in the A-pattern. The relationship was linear. By extrapolation the first 8 mm of superior oblique surgery had no effect but thereafter the effect obtained was 2 diopters reduction in A-pattern for every mm of superior oblique surgery. No similar correlation was found for the amount of recession performed measured indirectly. There was no correlation between reduction in superior oblique overaction and the amount of recession performed. This was believed to be due, at least in part, to an inaccurate system of measurement of superior oblique overaction. We now, therefore, measure superior oblique overaction in mm using the corneal light reflexes. There was, however, a good correlation between the amount of preoperative superior oblique overaction and the effect obtained.