Effects of Target Size and Test Distance on Stereoacuity

Abstract

Target size and test distance effects on stereoacuity were investigated in 24 subjects using a three-dimensional monitor.Examination 1: Target Size Effects. The test distance was 2.5 m for 0.1°, 0.2°, 0.5°, and 0.9° target sizes; crossed parallax was presented in 22-second units. Average stereoacuity values for 0.1°, 0.2°, 0.5°, and 0.9° target sizes were59.58±14.86,47.66±13.71,41.25±15.95, and39.41±15.52seconds, respectively. Stereoacuity was significantly worse with a 0.1° target than with 0.2°, 0.5°, and 0.9° target sizes (P=0.03,P<0.0001, andP<0.0001, resp.).Examination 2: Test Distance Effects. Test distances of 2.5, 5.0, and 7.5 m were investigated for a 0.5° target size; crossed parallax was presented in 22-second units. Average stereoacuity values at 2.5 m, 5.0 m, and 7.5 m test distances were44.91±16.16,34.83±10.84, and24.75±7.27seconds, respectively. Stereoacuity at a 7.5 m distance was significantly better than at distances of 2.5 m and 5.0 m (P<0.0001andP=0.02, resp.). Stereoacuity at a 5.0 m distance was significantly better than at 2.5 m (P=0.04). Stereoacuity should be estimated by both parallax and other elements, including test distance and target size.