Effects of Target Size and Test Distance on Stereoacuity

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 degrees, 0.2 degrees, 0.5 degrees, and 0.9 degrees target sizes; crossed parallax was presented in 22-second units. Average stereoacuity values for 0.1 degrees, 0.2 degrees, 0.5 degrees, and 0.9 degrees target sizes were 59.58 +/- 14.86, 47.66 +/- 13.71, 41.25 +/- 15.95, and 39.41 +/- 15.52 seconds, respectively. Stereoacuity was significantly worse with a 0.1 degrees target than with 0.2 degrees, 0.5 degrees, and 0.9 degrees target sizes (P = 0.03, P < 0.0001, and P < 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 degrees 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 were 44.91 +/- 16.16, 34.83 +/- 10.84, and 24.75 +/- 7.27 seconds, respectively. Stereoacuity at a 7.5 m distance was significantly better than at distances of 2.5 m and 5.0 m (P < 0.0001 and P = 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.