Abstract
PURPOSE: Rod-mediated dark adaptation delays are among the earliest functional abnormalities in age-related macular degeneration (AMD), preceding photoreceptor loss. This study evaluated whether parafoveal fundus-tracked dark adaptometry at 2 degrees detects earlier rod dysfunction than mid-macular loci (4 degrees and 6 degrees) and assessed the diagnostic performance of dynamic and steady-state parameters across eccentricities.
METHODS: In this cross-sectional study, 35 patients with predominantly early/intermediate AMD and 35 healthy volunteers across a broad range of ages underwent fundus-controlled dark adaptometry (S-MAIA-2; iCare/CenterVue) and multimodal imaging. After standardized bleaching, Goldmann III sized (0.43 degrees) cyan stimuli were presented 2 degrees, 4 degrees, and 6 degrees temporal to the fovea. Dark-adaptation curves were modeled to derive rod intercept time (RIT), final (rod) threshold (FT), and cone threshold (CT), each compared with normative data. Diagnostic accuracy was quantified using covariate-adjusted receiver operating characteristic (ROC) analyses, to account for age.
RESULTS: Among 70 analyzed eyes, RIT was abnormal in 86% of AMD eyes at 2 degrees, 69% at 4 degrees, and 60% at 6 degrees, whereas FT and CT were less frequently abnormal (29% to 51% and 17% to 26%, respectively). Median RIT at 2 degrees reached 60 minutes in the AMD cohort, indicating absence of rod function within the test duration in many eyes. RIT achieved the highest diagnostic accuracy, with covariate-adjusted area under the curve (AUC) values of 0.91 (95% credible intervals [CrI] = 0.80-0.97) at 2 degrees, 0.88 (95% CrI = 0.77-0.96) at 4 degrees, and 0.87 (95% CrI = 0.76-0.95) at 6 degrees.
CONCLUSIONS: Fundus-tracked dark adaptometry enables spatially precise assessment of parafoveal rod recovery. Parafoveal RIT prolongation represents the earliest and most frequent functional abnormality in AMD and demonstrates excellent diagnostic performance, supporting its potential as a sensitive functional biomarker for early disease and therapeutic trials.