Surgical management of unilateral elevator deficiency associated with horizontal deviation using a modified Knapp's procedure.

Both horizontal recti are transpositioned in unilateral elevator deficiency, leaving no alternative to correct any significant ipsilateral horizontal deviation. An effective method to correct vertical and horizontal deviations simultaneously is reported. A modified Knapp's procedure was performed by transposition of the superior half of equally divided (up to 15 mm) medial and lateral recti for vertical deviation and the inferior half after suitable recession or resection for horizontal deviation. This procedure was performed in ten patients who had type II unilateral elevator deficiency with horizontal deviation ranging from 18 to 45 prism diopters (PD). We were able to correct 20 PD of horizontal deviation and 25 PD of vertical deviation with a modified Knapp's procedure without any significant adverse effects after a follow-up of 21 months. A modified Knapp's procedure is recommended for unilateral elevator deficiency associated with horizontal deviation.