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Purpose: The vulnerability of rod photoreceptors in aging and early and intermediate age-related macular degeneration (AMD) has been well documented. Rod-mediated dark adaptation (RMDA) is a measure of the recovery of light sensitivity in rod photoreceptors following a bright light. Delays in RMDA during early and intermediate AMD have been widely reported. For RMDA's promise as an outcome for trials targeted at early and intermediate AMD to be realized, excellent test-retest reliability, its repeatability, must be established., Methods: Test-retest performance in a commonly used RMDA test based on the rod intercept time metric (RIT) was evaluated in participants with early and intermediate AMD and with normal retinal aging with testing approximately 2 weeks apart. The test target was placed at 5° eccentricity superior to the foveal center, an area with maximal rod loss in aging and AMD. Disease severity was identified by a trained and masked grader of fundus photographs using both the AREDS 9-step and Beckman classification systems. Bland-Altman plots and intra-class correlation coefficients (ICC) evaluated repeatability., Results: The analysis sample consisted of 37 older adults (mean age 76 years, standard deviation 5), with approximately one-third of the sample in each of three groups - normal aging, early AMD, and intermediate AMD. For the total sample, the ICC was 0.98. For individual AMD groups for both AREDS 9-step and Beckman classifications, the ICCs were also very high ranging from 0.82 to 0.99., Conclusion: We demonstrated that RMDA testing using the RIT metric has excellent repeatability when target location is at 5° in studying older adults from normal aging to intermediate AMD, suggesting the reliable use of this functional measure in trials.

Purpose: Photoreceptor (PR) outer segments, retinal pigment epithelium apical processes, and inter-PR matrix contribute to the interdigitation zone (IZ) of optical coherence tomography (OCT). We hypothesize that this interface degrades over adulthood, in concert with a delay of rod mediated dark adaptation (RMDA). To explore this idea, we determined IZ discernibility and RMDA in younger and older adults., Methods: For this cross-sectional study, eyes of 20 young (20-30 years) and 40 older (≥60 years) participants with normal maculas according to the AREDS 9-step grading system underwent OCT imaging and RMDA testing at 5° superior to the fovea. Custom FIJI plugins enabled analysis for IZ discernibility at 9 eccentricities in 0.5 mm steps on one single horizontal B-scan through the fovea. Locations with discernible IZ met two criteria: visibility on B-scans and a distinct peak on a longitudinal reflectivity profile. The frequency of sites meeting both criteria was compared between both age groups and correlated with rod intercept time (RIT)., Results: The median number of locations with discernible IZ was significantly higher (foveal, 4 vs. 0, p  = 0.0099; extra-foveal 6 vs. 0, p  < 0.001) in eyes of young (26 ± 3 years) compared to older (73 ± 5 years) participants. For the combined young and older sample, the higher frequency of discernible IZ was correlated with shorter RIT (faster dark adaptation) ( r s  = -0.56, p  < 0.0001). This association was significant within young eyes ( r s  = -0.54; p  = 0.0134) and not within older eyes ( r s  = -0.29, p  = 0.706)., Conclusions: Results suggest that the interface between outer segments and apical processes degrades in normal aging, potentially contributing to delayed rod-mediated dark adaptation. More research is needed to verify an age-related association between IZ discernibility and rod-mediated dark adaptation. If confirmed in a large sample, IZ discernibility might prove to be a valuable biomarker and predictor for visual function in aging.

Purpose: Studies on age-related macular degeneration often use rod-mediated dark adaptation (RMDA) to evaluate macular functional health, studying eyes with cataract and pseudophakic eyes within the same sample. We examine a poorly understood issue-whether rod intercept time (RIT), a measure of RMDA, changes after cataract surgery and intraocular lens (IOL) insertion as compared to RIT before cataract surgery. Cataract may serve as a filter reducing photo-bleach magnitude prior to surgery, biasing RMDA interpretation., Methods: A pre-/post-cataract surgery design was used. Persons with nuclear sclerotic and/or cortical cataract per the electronic health record were enrolled. Prior to cataract surgery, visual acuity, RMDA, and the LOCS III classification documenting cataract presence/severity were measured. Thirty days after surgery (mean), visual acuity and RMDA were repeated, followed by fundus photos to document macular health., Results: Twenty-four participants (mean age 72.7 years, standard deviation 5.6) enrolled. All eyes had nuclear sclerotic and nuclear color cataract; 68% had cortical cataract. All IOLs were monofocal with 21 having blue blocking characteristics and 3 had clear IOLs. Most eyes had higher RIT post-surgery (15.6 min, SD 6.7) as compared to pre-surgery (13.7 min, SD 6.4), p  = 0.0006, meaning that RMDA was slower post-surgery. Eyes with moderate cataract (<4 on any LOCS III grade) had RIT that increased on average by 0.7 min; those with more advanced cataract (≥4) had RIT that increased by 3.1 min ( p  = 0.0116). Results were unchanged when clear IOLs were removed from analysis., Conclusion: RMDA was significantly slower (RIT was greater) following cataract surgery, with the greatest impact on RIT in older eyes after surgery for more advanced cataract. These findings suggest that persons with more advanced cataract may bias results when evaluating RMDA using RIT.