Purpose: Although impairment of rod function in the early stages of age-related macular degeneration (AMD) has been well recognized, data on longitudinal changes in rod function at multiple retinal locations remain limited. This study investigated the longitudinal changes in retinotopic rod function in eyes with intermediate AMD (iAMD).
Methods: Complete ophthalmic examination, multimodal imaging, and scotopic perimetry were performed at baseline and at 12-month follow-up. Perimetric scotopic retinal sensitivities for the 505-nm stimulus were repeatedly measured for 20 minutes after exposing to a single photobleach (∼30%). The rod intercept time (RIT) and retinal sensitivity at seven retinal loci within the central 12° were ascertained. Using the 95% limit of measurement variability derived from the control eyes as a reference, the proportion of test points with a significant change in retinal sensitivity or RIT at follow-up was determined.
Results: Twenty iAMD and 6 control eyes were included. Decline in rod function was detected at 12-month follow-up in eyes with iAMD, but not in control eyes. Approximately 25% of test points in iAMD eyes showed a significant increase in RIT compared to 6% of test points with a decrease in RIT over the 12-month period (P < 0.001). Similarly, 40% of test points demonstrated a reduction in retinal sensitivity compared to the 7% of test points with an increase in retinal sensitivity at follow-up (P < 0.001).
Conclusions: There are detectable retinotopic changes in rod function over 12 months in iAMD eyes, indicating an ongoing disease progression in rod impairment or loss with time.