Scientists from the Shanghai Eye Diseases Prevention & Treatment Center and Tongji University (China) evaluated the short-term effects of different sunlight exposure on blood flow and perfusion of the fundus in their study.

In this parallel randomized controlled trial, 81 students aged 7–15 years with spherical equivalent refraction from −2.00 to +3.00 diopters were randomly assigned to a low-light group (4,000 lux) (N=40) or a bright-light group (10,000 lux) (N=41). Lux (“light”) is a unit of illuminance in the International System of Units (SI). 1 lux is the illuminance of a light flux of 1 lm uniformly distributed over an area of 1 m².

After 1 hour of indoor reading, participants received sunlight corresponding to their group’s intensity for 15 minutes. Blood flow and perfusion in the superficial retina, deep retina, and choroid were measured at four time points: before reading, after reading, and at 5 and 15 minutes of sunlight exposure.

During the first 5 minutes of sunlight exposure, the group receiving 10,000 lux showed a tendency to decrease perfusion and blood flow, especially in the choroid, while the group receiving 4,000 lux showed an increase. From 5 to 15 minutes, perfusion and blood flow of the fundus decreased in both groups. At the 5th minute, the group receiving 10k lux showed a greater decrease in the choroid (10k -0.4 vs. 4k 0.1, p=0.051). After 15 minutes of exposure, no significant difference was observed.

Scientists concluded that bright sunlight exposure can restore fundus perfusion and blood flow faster than low light exposure, but duration remains key. To prevent myopia, continuous sunlight exposure for more than 15 minutes is recommended to help restore fundus blood flow perfusion.

Link to the source:
https://bjo.bmj.com/content/early/2024/07/09/bjo-2024-325715?rss=1
Link to the full text of the article:
https://bjo.bmj.com/content/bjophthalmol/early/2024/07/09/bjo-2024-325715.full.pdf