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Y.-Z. Wang, C. Wilson; Effects of Aging and Age-Related Macular Degeneration (AMD) on the Detection of Global Structure From Noise Background. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5499.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies (Wang, Opt. & Vis. Sci., 78:447-454, 2001) showed that, over five decades, aging has less effect on shape discrimination sensitivity (18% loss) than on visual acuity (33% loss) or contrast sensitivity (81% loss). Since the patterns used in the previous study had both local and global cues to shape difference, the impact of aging on a pure global task is still unclear. In this study, we examined the effects of aging and AMD on pure global shape detection.
Ten normal young adults (mean age 33, mean acuity 20/15), 10 normal senior subjects (mean age 67, mean acuity 20/20) and 5 patients with AMD (mean age 75, mean acuity 20/32) participated in the study. The stimulus was composed of an array of Gabor patches. The global circular structure in the stimulus was defined by the tangentially-oriented coherent patches. Noise was introduced by randomly assigning orientation to patches. In a temporal 2AFC staircase paradigm where an array containing both coherent and noise patches was presented against a complete noise array, the subject's task was to judge which of two arrays contained a global circular structure. The array subtended a visual angle of 7.5 deg x 7.5 deg. The patch carrier spatial frequency was 6 cyc/deg. Coherent thresholds for detecting the global structure were estimated by a maximum likelihood fitting procedure.
The average coherent threshold+/-SEM of the young adult group was 10.3%+/-3.4%. This result was consistent with the finding in a previous study (Achtman, et al., J. Vis., 3:616-624, 2003). The average threshold (11.3%+/-1.0%) of the normal senior group was about 10% higher than that of the young group; no statistical difference in mean threshold was detected for these two groups (p=0.39). In comparison, the average threshold of the AMD group was 36.1%+/-9.3%, significantly higher than that of normal senior group (p=0.002).
Employing a purely global structure detection task, this study provides further evidence to support the hypothesis that global shape integration is much less affected by normal aging, but is disrupted by abnormal retinal input in AMD. Since the visual stimulus employed in this study covers a large part of the macula, it can provide a fast and sensitive test to quantify the functional integrity of the macula in patients with AMD.
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