The outdoor environment affects retinal and choroidal thickness

Purpose: Accumulating evidence suggests that time outdoors is protective against myopia development and that the choroid may be involved in this effect. The goal of this study was to examine the effect of 2 h of time outdoors in sunlight on retinal and choroidal thickness in adults.Methods: Twenty adults, ages 23- 46 years, each participated in three experimental sessions on different days, consisting of 2 h of exposure to (1) indoor illumination (350 lux), (2) darkness (< 0.1 lux) or (3) outdoor environment (6000- 50,000 lux). Spectral-domain optical coherence tomography (SD- OCT) imaging was conducted at baseline, after 1 and 2 h of exposure, and after 1 and 2 h of follow -up. Choroidal, total retinal, photoreceptor outer segment + retinal pigment epithelium (RPE) and photoreceptor inner segment thicknesses were determined.Results: At 2 h, the choroid was significantly thinner during the outdoor compared with the indoor and dark conditions (p < 0.01) but was not significantly different at follow -up. Total retinal thickness was significantly thicker during and after the outdoor compared with the indoor and dark conditions. The outer segment + RPE was significantly thinner during the outdoor compared with the indoor condition but was not significantly different at follow -up. The inner segment was significantly thicker during the outdoor compared with the indoor and dark conditions during exposure and follow -up.Conclusions: Spending 2 h outdoors under high-intensity sunlight resulted in an unexpected thinning of the choroid, which recovered post-exposure. Retinal thickness showed different responses to the outdoor and indoor environments and was sensitive to the duration of exposure.