Outdoor Exposure Influences Choroidal Changes Affecting Myopia Development

High-intensity sunlight may bring about short-term retinal and choroidal thickness changes, according to a study published in Ophthalmic Physiological Optics. While these findings cannot explain associations between short-term retinal and choroidal thickness changes during time spent outdoors and long-term changes associated with slowed axial growth, the report suggests that these findings may have implications for myopia. 

Researchers from the University of Houston included 20 adults (mean age, 27.7 years)  in the investigation and performed spectral-domain optical coherence tomography (SD-OCT) assessments at baseline and at 1 and 2 hours during exposure to 3 different environmental conditions, which included darkness (<0.1 lux), indoor illumination (350 lux), and outdoor exposure (6000-50,000 lux). The team performed 2 follow-up measurements at 1 and 2 hours following exposure during which participants remained indoors with lights on. Study participants underwent choroidal, total retinal, photoreceptor outer segment plus retinal pigment epithelium (RPE), and photoreceptor inner segment measurements while exposed to each condition and waited 5 to 15 days before repeating the trial with a different lighting condition. 

No choroidal thickness changes were observed for the indoor and dark environments, according to the report. During outdoor exposure, the choroid thinned significantly at 1 (P =.002) and 2 (P <.001) hours compared with baseline, but returned to baseline levels at the 2-hour follow-up (P =.63). Compared with the other conditions, choroidal thickness was significantly thinner outdoors compared with indoors (P =.004) or darkness (P =.007).

In the darkness, the retinal thickness was thinner at 1 and 2 hours (both P ≤.03) and returned to baseline levels at follow-up (both P =.89). Outdoors, the retinal thickness did not differ at 1 and 2 hours (both P ≥.05), but was thicker at follow-up (both P <.001). Compared with the indoor and dark conditions, retinal thickness was thicker during outdoor conditions at all time-points (all P <.05).

There were significant condition-by-time interactions for photoreceptor outer segment and retinal pigment epithelium (RPE) thicknesses (F_[8227.56], 15.49; P <.001) and photoreceptor inner segment thickness (F_[8211.33], 5.55; P <.001). In the outer segment, a significant pattern of thinning was observed in indoor and outdoor conditions at all timepoints (all P <.01). These measurements, however, were thicker in dark conditions at 1 and 2 hours (both P ≤.002). Compared between conditions, the photoreceptor outer segment plus RPE was significantly thicker in dark conditions compared with indoor or outdoor environments (all P <.001). For the inner segment, a general pattern of thickening was observed for indoor and outdoor conditions (all P <.05), except at 1 hour of indoor exposure, and no significant change was observed at any time point in the dark condition (both P ≥.10). Thicknesses differed significantly in outdoor conditions compared with indoor or dark conditions (both P <.001) and for the dark condition compared with the indoor condition (both P ≤.02). In general, recovery of the outer segment occurred faster than the inner segment during follow-ups.

 “[T]his study showed that spending time outdoors in sunlight induced choroidal thinning, which recovered by 2 h after returning indoors,” according to the researchers. “Retinal thickness exhibits differential responses under different environments, with greater thinning in the photoreceptor outer segment + RPE and greater thickening in the photoreceptor inner segment during outdoor exposure compared with indoor illumination and darkness. These findings will contribute to our understanding of how the retina and choroid respond to the outdoor environment, which has implications for eye growth and myopia.”

Study limitations include short duration and failure to examine refractive error.