Abstract
Abstract: :
Purpose: We previously reported a shape discrimination protocol that provides unique information about the integrity of the retinal sampling mosaic in early age–related macular degeneration (AMD). In this study, we adapt the protocol to a chart format that can be used routinely to screen for and monitor progression of AMD. The efficacy of this new shape discrimination chart was examined. Methods: Nineteen normal subjects (age 10 to 85 years, mean acuity 20/20) and 21 patients with macular degeneration (age 14 to 84 years with mean acuity of 20/60, 11 juvenile, 10 age–related) participated the study. Stimuli were radial frequency patterns. The computerized shape discrimination test was controlled by a temporal 2AFC staircase paradigm. Thresholds for detecting the radial modulation were estimated by a maximum likelihood fitting procedure. The handheld shape chart consisted of 16 groups of patterns. Each group had 4 patterns, 3 un–modulated and 1 modulated. The task was to indicate which of 4 patterns in a group was modulated (4AFC). A set of rules was used for the scoring of the chart test. Two versions of the shape charts were designed for test and re–test. All tests were performed monocularly. Results: For normal subjects, the mean±SD radial modulation threshold of the chart test was 0.32%±0.09, which was not significantly different from that of the computerized test (0.29%±0.10, p>0.33). There was also no significant difference between chart test and re–test scores (0.34%±0.10 vs. 0.30%±0.11, p>0.18). For the patients, the mean thresholds of the chart and the computerized tests were 0.66%±0.30 and 1.19%±1.41, respectively, and were significantly higher than that of normal subjects (p<0.009). For 5 patients with acuity worse than 20/100, the chart test underestimated the shape discrimination deficits. For 16 patients with acuity better than 20/100, the mean thresholds of the chart and the computerized tests were 0.58%±0.25 and 0.64%±0.37, respectively. Of 7 patients with 20/20 vision, 4 showed significant deficits in performing both tests. Conclusions: These results suggest that the new shape discrimination chart has the potential to be a useful screening tool for providing additional information about the integrity of the photoreceptor function in patients with macular degeneration. Further studies are needed to improve the chart for patients with severe loss of visual acuity.
Keywords: age–related macular degeneration • clinical research methodology • shape and contour