Short-term effects of sunlight exposure on fundus blood flow perfusion in children: a randomised controlled trial

Aim To evaluate the short-term effects of different sunlight exposure on fundus blood flow perfusion (BFP) after near work. Methods In this parallel randomised controlled trial, 81 students aged 7–15 with spherical equivalent refraction between −2.00 and +3.00 diopters were randomly assigned to either a low-illuminance (4k lux) group (N=40) or high-illuminance (10k lux) (N=41). Following 1 hour indoor reading, participants had sunlight exposure matching their group’s intensity for 15 minutes. BFPs in the superficial retina, deep retina and choroid were measured at four time points: pre-reading, post-reading, 5th-minute and 15th-minute sunlight exposure. Results Within the initial 5 minutes of sunlight exposure, the 10k lux group showed a tendency for decreased BFP, particularly in the choroid (superficial retina: −0.2, 95% CI −0.9 to 0.5; deep retina: −0.1, 95% CI −0.6 to 0.4; choroid: −0.4, 95% CI −0.8 to 0.0), while the 4k lux group exhibited an increase (superficial retina: 0.7, 95% CI 0.1 to 1.3; deep retina: 0.3, 95% CI −0.2 to 0.8; choroid: 0.1, 95% CI −0.2 to 0.5). From 5 to 15 minutes, BFP decreased in both groups. At the 5th-minute mark, the 10k lux group exhibited a greater decrease in choroid (10k −0.4 vs 4k 0.1, p=0.051). No significant difference was observed after 15 minutes of exposure. Conclusion Higher illuminance sunlight exposure can restore fundus BFP more rapidly than lower; however, duration remains pivotal. To prevent myopia, continuous sunlight exposure for over 15 minutes is recommended to aid in reinstating the fundus BFP increased by near work. Trial registration number NCT05594732 .