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Y.-Z. Wang, J. Furlan, G. Mitzel, Y.-G. He; The Effect of Macular Edema on Shape Discrimination Hyperacuity. Invest. Ophthalmol. Vis. Sci. 2010;51(13):547.
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Timely detection of conversion from early to exudative stage is crucial for successful treatment of age-related macular degeneration (AMD). Previously we reported that patients with high-risk early AMD have significant deficits in shape discrimination hyperacuity for detecting deformation of circular contours (Wang et al., 2002 IOVS, Vol. 43, p.2055). Here we investigate the impact of macular edema on the detection of shape distortion.
Eighteen eyes (mean VA 0.23±0.10SD logMAR) with macular edema associated with either exudative AMD or diabetic retinopathy and 16 eyes (mean VA 0.15±0.08 logMAR) with high-risk (large-size drusen) early AMD were included in the study on the basis of clinical and sdOCT documentation and VA 20/50 or better. A control group consisted of 20 age-matched normal volunteers (mean VA 0.07±0.08 logMAR, mean age 70±7 years). Visual stimuli were circular shapes distorted by modulating the radius sinusoidally. The mean radius was 1 deg. The peak spatial frequency was 3 cyc/deg. The shape discrimination test was controlled by a 2-interval forced-choice staircase paradigm. In each trial, subjects indicated which interval had the distorted shape. Radial modulation threshold was estimated with a maximum likelihood fitting procedure. Pelli-Robson contrast sensitivity test and Amsler grid test were also conducted.
The mean hyperacuity for detecting radial modulation were -0.19±0.15, -0.43±0.11, and -0.73±0.10 logMAR for the eyes with macular edema, high risk early AMD and normal controls, respectively. One-way ANOVA analysis indicated that there was a main effect of diagnostic group (F=90.9, p<0.001). Significant differences between mean thresholds were found among all groups (t≥5.3, p<0.001). When compared to the eyes with high risk early AMD, the eyes with macular edema showed 0.24 log unit loss in shape discrimination hyperacuity, but only 0.08 log unit loss in visual acuity (t=2.56, p<0.016), and no significant difference in letter contrast sensitivity (t=0.27, p=0.786). Abnormal Amsler grid perception was reported in 6 eyes of high risk early AMD and 8 eyes with macular edema.
The results support the hypothesis that large-size drusen or early stage macular edema may lead to the distortion of retinal images and in turn reduce patients’ ability to detect shape distortion in a forced-choice testing paradigm. The significant performance difference between the eyes with high-risk early AMD and with macular edema suggests that the shape discrimination hyperacuity may be an effective tool for detecting conversion from dry to wet form of AMD.
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