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B.J. Young, J.M. Wylie, S.B. Kaye; The Frisby Davis Distance (FD2) Stereotest Investigated at Different Distances Using Combined, Monocular and Binocular Depth Discrimination Thresholds . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5638.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To assess the performance of the FD2 test in terms of its monocular cue content. To determine at what test distances monocular cues reach threshold. To apply a method to treat monocular thresholds. Methods:Combined (CT) and monocular (MT) thresholds of depth discrimination were measured in 50 Subjects aged 21–62 years (mean 38 years) at 6m, 3m and 1m using the FD2 and at near using TNO and Frisby. Subjects were assessed using best corrected visual acuity at near and distance. A random sequence of testing was used. Testing distance was measured. The FD2 was placed at the correct measured height for each subject’s eye level and no head movement was allowed during testing. FD2 shapes were rotated between presentations. Subjects were required to correctly identify 3 out of 4 responses; a staircase procedure was used to determine the best depth discrimination. The binocular threshold (BT) of depth discrimination calculated, according to the function, BT=(1/CT–1/MT)–1. A repeated measures model was used for analysis using the logarithm of the BT. Results:Using the FD2, no subject achieved 3 out of 4 correct responses at 6m monocularly. The MT was measurable at 3m 10% (ranges: 140"– 200") and at 1m 60% (ranges: 952" – 2024"). Mean log BT were 1.14 (0.28), 1.47 (0.25) and 2.32 (0.10) at 6m, 3m and 1m, respectively. There was an association between age and depth discrimination, which followed a quadratic model (p=0.009). The linear associations between the FD2 and the TNO and Frisby tests, increased between 1m, 3m and 6m. Conclusions:By following correct procedures (accurate positioning of FD2 and avoidance of head movements) monocular cues at 6m do not reach threshold but reach threshold as test distance reduces. When MT fall within the range of the stereoacuity test, calculation of the BT from the CT and MT provides a satisfactory solution to give a reliable real depth distance stereoacuity.
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