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G. R. Jackson, J. G. Edwards, C. Owsley; A Short-Duration Dark Adaptation Protocol for the Detection of Age-Related Maculopathy. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2159. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Rod-mediated dark adaptation impairment is a clinical hallmark of early ARM and may be useful for detecting the earliest phases of disease or evaluating early treatment efficacy or prevention strategies. The utility of dark adaptometry as a clinical outcome or practical tool is hampered by a long test duration and high participant burden. Dark adaptation protocols typically have a test duration in excess of 40 minutes. The purpose of this study is to examine whether a 20-minute protocol can detect ARM.
9 normal old adults (mean age: 73 yrs) and 17 mild to moderate ARM patients (mean age: 76 yrs) (AREDS grades 2-9) participated in the study. Dark adaptation was measured using the AdaptDx, a novel dark adaptometer. The bleaching flash was a 4 deg diameter, 6.38 log scot td/sec circular field which was centered at 5 deg on the inferior vertical meridian. The stimulus was a 2 deg diameter 500-nm circular test target that was centered within the bleached area. A modified 3-1 staircase was used to estimate absolute threshold in the dark following bleaching. Approximately one threshold was measured each minute for 20 minutes. To estimate the speed of dark adaptation recovery, the rod intercept was estimated by linear interpolation from the dark adaptation curve. The rod intercept was defined as the amount of time for the patient's sensitivity to recover to 5.0 E-4 cd/m2.
The two groups had similar ages (p = 0.32). ARM patients exhibited substantially slower dark adaptation compared with normal old adults. The rod intercept for ARM patients (mean: 17.20 min, SD: 3.8) was on average, twice the duration of normal old adults' rod intercept (mean: 8.73 min, SD: 1.9) (p < 0.0001). Nine of the 17 ARM patients failed to obtain the criterion sensitivity within the 20-minute protocol, and were assigned a rod intercept of 20 min; thus the relative impairment between the two groups is understated. Eighty-eight percent of ARM patients exhibited a rod intercept that fell outside the normal reference range of normal old adults and all 9 normal participants' rod intercept were within normal limits.
Using a 20-minute protocol, ARM patients exhibit dramatic slowing of dark adaptation in comparison with normal old adults. The magnitude of the impairment compares favorably to lengthier protocols that required 60 to 90-minutes used in our prior research. The substantial dark adaptation impairment exhibited by the ARM group suggests that further optimization will considerably shorten the duration of the test without sacrificing sensitivity.
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