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J. V. Odom, M. J. Leys; Effects of Age and Low Vision on Coherence Thresholds in Rotational Optic Flow Patterns (Curl). Invest. Ophthalmol. Vis. Sci. 2009;50(13):2533.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the coherence thresholds for direction of rotation judgments (curl) in four groups of subjects, young normals, older normals, and low vision patients with either central visual field loss due to age-related macular degeneration (AMD) or diabetic retinopathy (DR).
Four groups of subjects were tested; younger normals aged 21-50 years, older normals aged 60 years or more, low vision patients with AMD aged 60 years or more, and low vision patients with DR. Observers were seated 50 cm from a display that subtended 44.6 arc deg in the horizontal dimension. The observer saw a red line at the center of the screen. Pressing a mouse button began a of 833 mS trial during which the stimulus was an optic flow pattern of 100 white dots on a black background. Dots had a lifetime of 467 mS or were replaced if they moved off of the screen. Dot velocity was 1.261 deg/S. At the end of the trial the central red line reappeared. The observers’ indicated the direction of rotation, clockwise or counterclockwise, of the dots by pressing either the left or right mouse button. On the first trial all 100 dots moved in the same direction, clockwise or counterclockwise. Correct judgments resulted in a reduction in the number of dots moving in the same direction (coherently) and an increase in the number of dots which moved in other randomly selected directions. A staircase procedure using a two-down, one-up rule was employed to determine the threshold number of coherently moving dots which were required for subjects to accurately determine the direction of rotation of the coherently moving dots. Data were analyzed using an ANOVA with age as a covariate. A significant ANOVA was followed by post hoc comparisons of means.
Young normals had an average coherence threshold of 9.5%, the average threshold for older normals was 17.15%, for DR patients was 17.34% and for AMD patients was 42.64% (p = 0.003).
Important differences exist in the perception of curl among patients with low vision. AMD patients have poorer perception of coherence than DR patients or similarly aged patients. Although age affects perception of curl, age does not appear to account for the difference in patient groups. Detection and discrimination of curl is thought to be important in the control of balance. Impaired curl perception may be related to poorer balance and increased falls in the elderly and particularly patients with AMD.
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