Light exposure elicits an increase in OR thickness as measured by OCT in mice and humans; the procedure has been previously published.22 (link)–24 (link, link),26 (link) Briefly, after anesthetizing mice with ketamine (100 mg/kg) and xylazine (6 mg/kg), retina OCT images were captured with Envisu UHR2200 (Bioptigen, Durham, NC, USA), with OCT beam bandwidth of 160 nm, and theoretic axial resolution of 1.6 μm in tissue. The mouse eye was positioned with the optic nerve head (ONH) in the center of the OCT scan. Full-field (50° fixed field view, corresponding to 1.4 mm × 1.4 mm for a typical mouse eye) volume scans (at 1000 A-scan × 100 B-scan × 5) and a vertical B-scan (averaged 40 times) were collected. Mice used in this study were of similar age, so between-mice eye size differences were small. Vertical B-scan images were studied from our previous results showing that d-cis-diltiazem produces oxidative stress in superior and inferior retina,9 (link) and OR thickness was measured at location ∼450 μm superior (“12-o'clock” position) and ∼450 μm inferior (“6-o'clock” position) to the center of the ONH, by using vendor-provided Reader program (Bioptigen) and an in-house MATLAB program. OR length was measured from external limiting membrane (ELM) to the RPE-choroid boundary.