Systematic Underestimation of Visual Sensitivity Loss on Microperimetry: Implications for Testing Protocols in Clinical Trials.

Abstract

To examine whether systematic changes in visual sensitivity measurements on microperimetry occur over tests within the same session and whether these changes vary according to the level of visual sensitivity loss. Eighty individuals with glaucoma or atrophic age-related macular degeneration underwent three microperimetry tests in one eye during one session using the 4-2 staircase strategy. Changes in mean sensitivity (MS) and pointwise sensitivity (PWS) between the first and second test pairs were examined, with PWS was examined separately based on its average value across the three tests in 6-dB bins. The coefficient of repeatability (CoR) for MS between each sequential test pair was also calculated. There was a significant decline in MS from the first to second test (P = 0.001), but no significant difference in MS was seen between the second and third tests (P = 0.562). This significant decline in the first test pair was observed in locations with an average PWS of <6 dB or between 6 to 12 dB and between 12 to 18 dB (P < 0.001), but not for all other average PWS bins (P ≥ 0.337). The CoR of MS was significantly lower in the second compared to the first test pair (1.4 dB and 2.5 dB, respectively; P < 0.001). The 4-2 staircase strategy conventionally used on microperimetry testing systematically underestimates visual sensitivity loss on the first test. The consistency and accuracy of visual sensitivity measurements on microperimetry in clinical trials could be markedly improved by using estimates from an initial test to seed subsequent tests and excluding this first test from analyses.