It is feasible to use a DAC perimeter to study dark-adapted static and dynamic rod-mediated function at multiple retinal loci. Static and dynamic rod function were abnormal in intermediate AMD and more so in eyes with RPD, particularly within the central 6° retina.

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 128 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.

To quantify the association between dark adaptation parameters and other clinical measures of visual function among people with and without early and intermediate age-related macular degeneration (AMD). Methods: In this cross-sectional study, participants underwent multimodal imaging and visual function testing, including best-corrected visual acuity (BCVA), lowluminance visual acuity (LLVA), low-luminance deficit (LLD = BCVA-LLVA) and the 10-item Night Vision Questionnaire (NVQ-10). Dynamic and static dark-adapted chromatic perimetry (DACP) was performed. Sensitivity difference was defined as the difference in sensitivity between the 505-nm and 625-nm stimuli. Rod intercept time (RIT) was estimated as the time required to reach a threshold of −3 log candelas/meter 2 with the 505-nm stimulus following bleaching. The magnitude of association between the DACP parameters and other clinical tests was estimated via mixed-effects regression. Results: A total of 51 participants (aged 51-88 years, 65% female, 39% with AMD) were included. RIT was found to be negatively associated with BCVA (P < 0.001), LLVA (P = 0.005), and NVQ-10 score (P = 0.028) but not LLD (P = 0.763). There was no evidence of an association between sensitivity difference and any of the clinical measures (P ≥ 0.081). Conclusions: Reduced rod function, as determined by RIT, was associated with lower NVQ-10 scores (designed to interrogate rod-mediated function) and with worse BCVA and LLVA (measures of cone function). Translational Relevance: Decreasing rod function maybe indicative of more generalized photoreceptor dysfunction involving cones. Further development of questionnaires to target function in scotopic conditions may provide an easier to administer test without the need to perform perimetric tests of rod function.