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Progression of Dark-Adapted Visual Fields Over 3 Years in the Rate of Progression in USH2A-Related Retinal
David G Birch1, Jacque L Duncan2, Lassana Samarakoon3
1Retina Foundation of the Southwest, Dallas, Texas, United States.
Purpose:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
