Repeatability of Scotopic Sensitivity and Dark Adaptation Using a Medmont Dark-Adapted Chromatic Perimeter in Age-related Macular Degeneration

Purpose Functional studies of rods in age-related macular degeneration using the Medmont Dark-Adapted Chromatic Perimeter (DACP) have demonstrated impairments in scotopic sensitivities and dark adaptation (DA). We investigated the intersession repeatability of scotopic sensitivity and DA parameters including the rod intercept time recorded from the Medmont DACP. Methods Scotopic thresholds (14 test points) and DA using a 30% photobleach (eight test points) were measured on two separate days from participants 50 years of age or older with a range of age-related macular degeneration severity at loci superior and inferior to the fovea. Repeatability coefficients were calculated for prebleach scotopic sensitivity, and for DA parameters including rod intercept time. Results Twelve participants (mean age, 79.7 ± 8.1 years) repeated Medmont DACP testing within 50 days. Repeatability coefficients for prebleach scotopic sensitivity to long wavelength (red, 625 nm) and short wavelength (cyan, 505 nm) were 5.9 dB and 7.2 dB, respectively. The DA curve-derived repeatability coefficients for cone threshold was 3.9 dB, final threshold 5.3 dB, with an R value of 0.075 decades/min, rod intercept time 7.6 minutes, and RITslope 0.54 min/degree. Conclusions This study establishes repeatability coefficients for scotopic thresholds and multiple DA parameters obtained with the Medmont DACP in patients with age-related macular degeneration. These repeatability coefficients will serve as the basis for determining clinically meaningful change in rod function in future clinical trials. Translational relevance Measures of repeatability parameters of scotopic thresholds and DA are essential to the accurate interpretation of results in future studies and trials using these measures.