Effect of interocular difference in retinal illuminance on monocular and binocular flicker perception

Abstract

Purpose : Detection of luminance-modulated flicker under monocular and binocular viewing conditions worsen with a reduction in retinal illuminance.The impact of interocular difference in retinal illuminance on these thresholds however remain unknown.This study investigated the impact of purposely-induced variations in retinal illuminance of one or both eyes on monocular and binocular flicker modulation thresholds (FMTs) and on the binocular summation ratios (BSRs) of flicker.

Methods : Monocular and binocular FMTs were measured using the Flicker-Plus test for 30’ target at fovea and four parafoveal (5^o) locations in 10 healthy adults at a baseline retinal illuminance of 930Td (7mm pupil diameter) and with 10 to 80% (827 to 186Td) induced interocular difference in retinal illuminance using neutral density filters over one eye,all in random order. The measurements were repeated in 5 subjects with bilateral change in retinal illuminance from 388 to 1553Td. BSRs were calculated by dividing the monocular threshold of the non-attenuated eye (for interocular difference condition) or the better eye (for bilateral condition) to the binocular threshold.

Results : The mean (±1SE) non-attenuated monocular foveal and parafoveal FMT was 2.98±0.28% and 5.3±0.63% respectively. These FMTs increased with reduction in monocular retinal illuminance (3.71±0.73% to 6.2±0.9%) and with increasing interocular difference in retinal illuminance(1.99±0.35% to 3.19±0.76%)(p<0.05, for both).The resultant BSRs were thus larger for interocular differences <50% (1.56±0.12) than for those ≥60% (1.27±0.13) (p≤0.01).This trend remained the same in the parafoveal region. Monocular(3.83±0.1% to 3.0±0.12%) and binocular(1.84±0.1% to 1.82±0.09%) FMTs and BSRs (1.68±0.1) remained largely stable with bilateral reduction in retinal illuminance.

Conclusions : The worsening of binocular flicker detection capability is proportional to its monocular value up to 50% of interocular difference in retinal illuminance. Beyond this range, the binocular loss is proportionally greater than the monocular loss, leading to a reduction in binocular summation of flicker. These results are in agreement with the negative impact of naturally-occurring interocular differences in monocular FMTs on binocular summation of flicker, observed in our earlier study.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.