Pilot Study of the Effects of Ambient Light Level Variation on Spectral Domain Anterior Segment OCT-Derived Angle Metrics in Caucasians versus Asians

Abstract

ABSTRACTPurpose: To investigate the effects of ambient light level variation on spectral domain anterior segment optical coherence tomography (SD-ΟCT)-derived anterior chamber angle metrics in Caucasians versus Asians.Materials and Methods: Caucasian (n = 24) and Asian participants of Chinese ancestry (n = 24) with open angles on gonioscopy had one eye imaged twice at five strictly controlled, ambient light levels. Ethnicity was self-reported. Light levels were strictly controlled using a light meter at 1.0, 0.75, 0.5, 0.25, and 0 foot candle illumination levels. SD-OCT 5-line raster scans at the inferior 270° irido-corneal angle were measured by two trained, masked graders from the Doheny Image Reading Center using customized Image-J software. Schwalbe’s line-angle opening distance (SL-AOD) and SL-trabecular iris space area (SL-TISA) in different light meter readings (LMRs) between the two groups were compared.Results: Baseline light SL-AOD and SL-TISA measured 0.464 ± 0.115mm/0.351 ± 0.110mm2 and 0.344 ± 0.118mm/0.257 ± 0.092mm2, respectively, in the Caucasian and the Asian group. SL-AOD and SL-TISA in each LMR were significantly larger in the Caucasian group compared to the Asian group (p < 0.05). Despite this difference in angle size between the groups, there were no statistically significant differences in the degree of change in angle parameters from light to dark (% changes in SL-AOD or SL-TISA between the two groups were statistically similar with all p-values >0.3).Conclusion: SL-based angle dimensions using SD-OCT are sensitive to changes in ambient illumination in participants with Caucasian and Asian ancestry. Although Caucasian eyes had larger baseline angle opening under bright light conditions, the light-to-dark change in angle dimensions was similar in the two groups.