By Linda Conlin, Pro to Pro Managing Editor

Research has shown a direct correlation between long-term sunlight exposure and a decrease in the incidence of myopia in children. But are there immediate effects? A recent study from Shanghai, published in the British Journal of Ophthalmology showed immediate effects of sunlight exposure on fundus blood flow perfusion (BFP) after near work.

Blood perfusion is the local fluid flow through the capillary network and extracellular spaces of living tissue. It is vital for normal tissue physiology and is responsible for the transport of oxygen, nutrients, and waste products. During near work, the retina needs increased energy, which increases BFP. The altered fundus blood flow is considered to play a role in the development of myopia and so can be a predictor for myopia. The study showed that sunlight exposure reduced the elevated BFP. ( Zhao L, Zhang B, Wang J, et al Short-term effects of sunlight exposure on fundus blood flow perfusion in children: a randomised controlled trial British Journal of Ophthalmology Published Online First: 09 July 2024. doi: 10.1136/bjo-2024-325715)

The study included 81 students—ages seven to 15 years—with spherical equivalent refraction between −2.00D and +3.00D. Following one hour of indoor reading, each participant had 15 minutes of sunlight exposure. Study authors measured blood flow perfusions in the superficial retina, deep retina, and choroid at four time points—pre-reading, post-reading, and at the fifth minute and 15th-minute of sunlight exposure. Data showed that within the initial five minutes of sunlight exposure the subjects had a tendency for decreased BFP, particularly in the choroid, and from five to fifteen minutes, the investigators observed a greater decrease in BFP. As the BFP in both the retinal and choroidal layers increased after 1 hour of intense near work, in the outdoor environment with less visual processing, in conjunction with the effects of sunlight, the demand for oxygen decreased, resulting in reduced perfusion levels. The study results indicated that the duration of sunlight exposure is pivotal in restoring BFP.

“Our study emphasizes that sunlight exposure can effectively counter the increase in fundus BFP due to near work,” the study authors noted in their BJO paper. “Sunlight with higher illuminance can restore fundus blood flow more rapidly than lower illuminance, but the duration of exposure remains a critical factor. To prevent myopia, continuous exposure to sunlight for 15 minutes or more is recommended to aid in reinstating the fundus blood flow increased by near work.”