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J. V. Odom, J. O. Mali, M. J. Leys; Heading Precision in Age-Related Macular Degeneration (AMD): Effects of Directional Noise. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3619.
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Our previous research indicated that noise had little effect on heading precision of normals and diabetic retinopathy patients, but affected AMD patients with 20/60 or worse binocular best corrected visual acuity (BBCVA). We tested the effects of noise on thresholds of treated AMD patients with BBCVA of 20/40 or better to determine if factors other than acuity cause the loss. Normal groups aged either 21-59 years or 60 years or more and AMD patients with 20/60 or worse BBCVA were compared to the new AMD group.
Observers were seated 50 cm from a display that subtended 44.6 arc deg horizontally. White dots on a black background appeared at random locations and moved away from a focus of expansion (FOE). The observers’ task was to determine if the FOE was to the right or left of center. A double staircase was employed to determine a threshold precision for the FOEs. Threshold precision was ½ the difference of the staircase thresholds. Observers repeated the judgments under 4 conditions: a no noise condition and 3 conditions in which the individual flow vectors were perturbed by Gaussian noise along the x-axis. The noise standard deviation (SD) varied from 0.92 to 2.75 deg.
ANOVA indicated significant effects of group, noise and their interaction (p<0.01). Without noise, there was no significant difference in heading precision between the AMD groups and the older normals (p > 0.10). Older normals had higher thresholds than younger normals; however, increasing noise did not increase thresholds in either normal group over the range tested, i.e., the slope of the functions relating noise to precision did not differ from 0 (p > 0.1). However, as noise levels increased, heading precision thresholds increased for the AMD groups. The greatest differences between groups occurred at the highest noise level (p < 0.01); i.e., in both AMD groups the slopes differed statistically from 0 (p < 0.03).
Noise with a SD up to 2.75 deg does not impair heading precision in normals but does impair that of AMD patients, even if their BBCVA is 20/40 or better. Poor BBCVA is not be the only cause of impaired precision of heading judgments in AMD patients.
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