Distance Stereopsis in Clinical Practice

Abstract

Abstract: : Purpose:Assessment of distance stereopsis in adult patients with ocular motility disturbances in an outpatient clinical situation. Methods:100 patients with disturbances of ocular motility were included. Stereoacuity was measured at distance with the Frisby Davis Distance Stereotest (FD2). Stereoacuity was also measured at near. A staircase procedure was used to measure stereoacuity threshold. Stereoacuity measurements were analysed as the logarithm of the threshold angle. Visual acuity was recorded in LogMAR units. Results:Ages ranged from 16years to 89years (mean 59.89years SD 18.33). Stereoacuity was demonstrated in 92% of patients, 64% at distance and 78% at near. Mean stereoacuity at distance was 28.13" (1.37log (0.28)) and near 178.99" (2.08log (0.43)). There were 50 patients with horizontal deviations, their distance stereoacuity (1.44) was significantly better than their near stereoacuity (2.17) (Dif 1.1, p<0.05). 28 patients had vertical deviations and 9 with mixed vertical and horizontal deviations. The patients with vertical deviations were divided into those with either underaction of elevation or depression. Those with weakness of depression had significantly better distance than near stereoacuity (p<0.05) and conversely there was a trend for near to be better than distance in those (12) with weakness of elevation. There were 13 patients with other ocular disorders e.g. Homonymous Hemianopia. 65% of all the patients showed better distance than near stereopsis. A proportion (8 patients) who had no demonstratable stereopsis at near, showed consistent distance stereoacuity (mean 37.7 SD 14.14). There were 9 patients with mixed horizontal and vertical deviations. There was no significant difference between their distance (1.39) and near (2.12) stereoacuity. Conclusions:Adult patients with ocular motility disturbances who have no apparent stereopsis using a near stereoacuity test had measurable distance stereoacuity in clinical practice. Patients with weakness of elevation performed better with near stereoacuity tests, while those with a weakness of depression performed better with a distance stereoacuity test. This may be due to the lower level at which near tests are positioned. Measuring distance stereopsis identifies groups of patients who would otherwise have had no demonstratable stereopsis using only near relative object stereoacuity tests in 8%.

Keywords: binocular vision/stereopsis • depth • detection