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J. O. Mali, M. J. Leys, J. V. Odom; Coherence Thresholds in Rotational Optic Flow Curl: Effects of Binocular Visual Acuity of Age-Related Macular Degeneration (AMD). Invest. Ophthalmol. Vis. Sci. 2010;51(13):3620.
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To compare the coherence thresholds for rotational direction of motion in AMD patients with normal binocular best corrected visual acuity (BBCVA) and AMD patients with binocular central vision loss (BCVL) to similarly aged normal subjects.
Four groups of subjects were tested: normals aged 21-50 years, normals aged 60 years or more, AMD patients with normal BBCVA, and AMD patients with BCVL (i.e., 20/60 or worse BBCVA). Observers were seated 50 cm from a display that subtended 44.6 arc deg horizontally. The observers’ task was to determine the direction of rotation, clockwise or counterclockwise, from an optic flow pattern display of 100 white dots on a black background. On the first trial, all dots moved in the same direction, clockwise or counterclockwise (100% coherence). A staircase procedure using a two-down, one-up rule was employed to determine the threshold percent of coherently moving dots required for subjects to accurately determine the direction of rotation (curl).
There was a significant difference in the ability to detect curl among the four groups (p = 0.029). On average, young normals required 9% coherence, older normals 16%, AMD with normal vision 20%, and AMD patients with BCVL 43%. The AMD group required greater coherence (more dots) in order to correctly judge rotational optic flow curl (p = 0.036). Curl threshold is correlated strongly with BBCVA (r = 0.56, p < 0.01) in this sample.
While it has been shown that AMD with central visual loss has a major impact on judgments of curl direction, it seems that AMD patients with normal BBCVA (visual acuity of 20/40 or better) did not require a statistically significantly larger percent of coherently moving dots to detect the direction of curl than did normal patients of similar age. The significant impairment of judgment of curl direction appears to be associated with binocular central vision loss.
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