Recognition Time after Four Muscle Recession for Nystagmus

Abstract

Large recession of the four horizontal rectus muscles has been shown at best to minimally improve visual acuity as measured with Snellen letters. However, many patients have reported a dramatic improvement in ability to recognize objects more quickly after large recession of the horizontal recti. We used a shutter device to measure the time it took six patients with nystagmus to recognize a projected Snellen “E” at the threshold of their vision before and after the four muscle recession surgery. Three control patients with nystagmus but not having had surgery were measured twice, two months apart. The mean preoperative time needed to correctly recognize the orientation of the tumbling “E” (recognition time) was .50 secs. (range 0.40 to 0.80) and the two month postoperative recognition time was 0.20 secs. (range 0.10 to 0.40). The mean initial recognition time for the control patients was 0.30 secs. and the mean repeat recognition time was 0.50 sees. These results indicate that the four muscle recession for nystagmus decreases the time necessary to recognize projected figures and therefore improves visual function measured in a non-traditional manner, and supports patient reports of improved vision which cannot be confirmed by improved snellen acuity.

• nystagmus
• surgery
• recognition time