Progression of Dark-Adapted Visual Fields Over 3 Years in the Rate of Progression in USH2A-Related Retinal Degeneration (RUSH2A) Study

To document the time course of visual sensitivity loss in dark-adapted visual fields (DAVF). To explore longitudinal relationships between DAVF measured using two-color dark-adapted chromatic and rod function from electroretinogram (ERG) and full-field stimulus testing in the RUSH2A study. Full-field rod mean sensitivity, number of rod loci, maximum sensitivity, DAVF V30 were measured in one eye for DAVF ancillary study participants at the RUSH2A 12-month, 24-month, 36-month and 48-month visits. Loci where cyan relative to red sensitivity was greater than 5 dB on dark-adapted chromatic perimetry were considered rod mediated. Correlation coefficients (r) between changes in DAVF measures with changes in standard clinical measures were estimated. Among 38 participants with evidence of rod function, the annual rate of loss (outlier down-weighted) of DAVF mean sensitivity and total volume were -1.08 dB/year and -2.8 dB-sr/year, respectively. Change in full-field rod mean sensitivity was highly correlated with change in DA 0.01 ERG (r = 0.79; P = 0.049). Younger participants showed greater change over time in DAVF measures. Average yearly change in mean DAVF measures was comparable with the annual change on full-field stimulus testing and faster than in cone-mediated measures. Two-color DAVFs identified rod-mediated function in the majority of patients with USH2A mutations, even though many showed no evidence of rod ERG function.