Reliability and consistency of dark-adapted psychophysical measures in advanced eye disease

To establish reliable vision measures allowing functional monitoring in patients with severe vision loss.

Legally blind and normally sighted subjects were enrolled in a repeated-measures study to determine the reproducibility of psychophysical vision measures under scotopic conditions. The tests included dark adaptometry, dark-adapted, full-field flash testing, and dark-adapted macular thresholds, obtained by using a perimeter with 500- and 650-nm targets. Two to five test repetitions were performed on the better eye of each subject at monthly intervals. Subject groups included retinitis pigmentosa (RP; n = 33), macular disease (MD; n = 14), optic nerve disease (ON; n = 4), diabetic retinopathy (DR; n = 5), and other retinal diseases (OR; n = 9), and normally sighted control (CTL; n = 12).

Dark adaptometry timing yielded mean coefficients of variation for subjects across all groups that averaged approximately 20% throughout the test. For dark-adapted perimetry, the coefficients of repeatability (CR(.95)) were <7 dB (CTL), <8 dB (OR), <6 dB (ON and RP), and <15 dB (MD). Full-field flash test CR(.95) by group varied from 5 to 15 dB, and most low-vision groups performed more reliably than CTL subjects.

Dark-adapted psychophysical tests can provide reproducible vision measures in subjects with severe visual impairments, and these tests would be useful in monitoring outcomes in future clinical trials to reverse, halt, or slow vision loss. The most valuable measure of remaining vision was the dark-adapted, full-field flash test, as it produced repeatable results at all levels of vision loss and for all disease states included in this study.