Repeatability and Comparison of Dark Adaptation Using the Medmont DAC Perimeter and AdaptDx Dark Adaptometer
Durin Uddin, Dr. Brett Jeffrey, Dr. Wiley Henry, Dr. Tiarnan Keenan, Dr. Oliver Flynn, Dr. Wai Wong, Dr. Emily Chew, Dr. Catherine Cukras
NEI
Introduction: Functional studies of dark adaptation (DA) in age-related macular degeneration (AMD) using the Medmont Dark-Adapted Chromatic Perimeter (DACP) and AdaptDx dark adaptometer have demonstrated impairments in rod-mediated kinetics. We compared the rod intercept times (RITs) obtained at two retinal loci on the AdaptDx with RITs obtained using the Medmont DACP. We also investigated the repeatability of RIT measures for the Medmont DACP.
Methods: Participants >50 years of age, with a range of AMD severity, had dark adaptation testing on the Medmont DACP and AdaptDx within 30 days of each other. DA was measured with the Medmont DACP at 8 loci (4°,6°,8°,12° superior and inferior) along the vertical meridian after a 30% bleach. DA was measured using the AdaptDx protocol either at 5° superior to the fovea or at 12° (using a reduced bleach flash). Rod intercept time (RIT) defined as the time to detect a -3.1log cd/m2 green stimulus (500/505 nm) was measured. Bland-Altman plots were used to compare RITs measured at 4° and 6° superior on the Medmont DACP to RITs measured at 5° on the AdaptDx; RITs at 12° were also compared.
Results: DA was measured in 45 participants (mean age=76.4±9 years) with a range of AMD severity (no AMD n=18, intermediate AMD n=20, subretinal drusenoid deposits n=7). Longer RITs were observed on the AdaptDx 5° than either the Medmont 4° (n=37, mean difference ±SD = -2.4±4.1 min) or 6° (-3.5±4.2 min). Shorter RITs were observed on the AdaptDx 12° than the Medmont but with similar SD (n=9, 6.9±5.1 min). Twelve participants (79.7±8 years) repeated Medmont DACP testing within a 50-day period. A Bland-Altman plot of RITs across all retinal eccentricities demonstrated that RIT was reproducible with a mean RIT difference of -0.57±3.8 minutes.
Conclusion: The methods used by Medmont DACP and AdaptDx for measuring DA vary (e.g. bleach and stimulus delivery) yet very similar rates of DA, as measured by RIT values, were found for both instruments when measured at similar retinal eccentricities. The mean differences in RIT between the instruments indicate a systematic bias which could be attributed to different methodology such as bleach delivery and/or different curve fitting. The SD between AdaptDx and Medmont instruments is similar to that found previously when studying the repeatability of the AdaptDx prototype, indicating similar reproducibility in these two instruments.