Effectiveness of inferior transposition of the horizontal rectus muscles for acquired inferior rectus paresis.

Full inferior transposition of the horizontal recti (inverse Knapp procedure) was performed on four patients with unilateral inferior rectus muscle weakness. The patients were followed up over time to determine the medium- and long-term effectiveness of the procedure. All of the patients had single binocular vision without the use of prisms in the primary position of gaze and three in the reading position after a mean postoperative follow-up interval of 21/2 years. The mean primary position preoperative vertical deviation was 20.3 delta and the mean primary position postoperative vertical correction was 19.5 (range, 16 to 24) delta. The field of binocular single vision was assessed quantitatively and scored 2.4% preoperatively compared with 52.3% postoperatively. There was no decrease in the effect of the procedure over time. Additional surgery may still be required to correct symptomatic residual vertical down-gaze diplopia.