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J. R. House, S. Y. Woo, J. Tong, H. E. Bedell; A Test of Orientation Discrimination Distinguishes Between Eyes With and Without Observable Macular Changes That Precede AMD. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2175.
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© ARVO (1962-2015); The Authors (2016-present)
Orientation discrimination for randomly positioned line segments was assessed as a potential indicator of subtle macular changes that precede early AMD.
A masked examiner categorized 50 eyes of 25 patients aged 52 - 79 as at risk for early AMD (N = 29) or normal (N = 21), based on the presence or absence of macular drusen and/or early RPE changes in fundus photographs. Visual acuity ranged from 20/15 to 20/40+1, with a median value of 20/20 in both groups of eyes. To measure orientation discrimination, two 1-deg patches of 0.4-deg lines were presented for 200 ms on opposite sides of a central fixation spot. In one patch, all of the lines were parallel. In the other, each line varied from the mean orientation by a pre-determined angular standard deviation. After each presentation, the patient indicated which patch contained the more parallel lines. The orientation threshold was determined from a psychometric function, fit to the responses to 80 trials. Amsler grid testing and automated 10-2 perimetry were performed also for each eye.
Average orientation thresholds were nearly twice as high in at-risk compared to normal eyes (9.1±3.6 deg vs. 4.9±1.5 deg; p=1.9e-6). Thresholds in 17 of the 29 at-risk eyes were higher than 95% of the normal eyes. Response errors were distributed non-uniformly by target meridian in 9 of the at-risk eyes, suggesting that retinal disruption was de-centered with respect to the fovea. In contrast, none of the normal eyes showed a non-uniform distribution of errors. Amsler grid responses were abnormal in 2 at-risk eyes and 1 normal eye. Central field defects (p<0.01) with 10-2 perimetry occurred with equal probability (20%) in the at-risk and normal eyes.
In contrast to Amsler grid and automated central-field testing, psychophysical orientation discrimination distinguishes between eyes with and without subtle age-related macular changes.
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