Japanese researchers link outdoor time to rapid increase in choroidal thickness

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Japanese researchers reported that short, intensive outdoor activity for only 1 week increased the choroidal thickness in Japanese schoolchildren. This is the first such study to report the effects of short-term outdoor activity on the choroidal thickness,¹ according to first author Mamoru Ogawa, MD, who is from the Department of Ophthalmology and the JINS Endowed Research Laboratory for Myopia, Keio University School of Medicine, Tokyo.

The rapidly increasing prevalence of myopia and its progression have been recognized,^2,3 therefore, expedited intervention against myopia progression from childhood and the development of a new therapeutic strategy are urgently needed, Ogawa and colleagues emphasized.

They looked at the effects of outdoor activity as a potential intervention in the myopia pandemia. “Outdoor activity is an evidence-based environmental factor that retards myopia progression.⁴ Previous studies have provided evidence that lighting prevents myopia progression in animals even for a short intensive period.^5-7 Wu et al.⁸ reported that school-based intervention of 2 hours outside over the course of a year prevented myopia progression,” they explained.

Because the choroidal thickness is correlated with myopia and axial lengths (ALs),⁹ the researchers expected that the choroidal thickness is a predictor of myopia, because previous studies showed that the elongation followed choroidal thinning in mice and humans.^10-12

Camp study and results

The investigators conducted aninstitution-based prospective observational study aims to assess the impact of outdoor activity for 1 week during a camp program to study ocular parameters including the choroidal thickness.

The intensive outdoor activity program included an average of 6.15 ± 2.98 hours of daily time spent outdoors on subsequent days for 1 week at a low-altitude (1,738 feet) mountain camp. Twenty-four children (50% girls; mean age, 11.5 ± 0.5 years) participated in this program, the investigators recounted.

Eye examinations were conducted at baseline and at the end of the program that included measurement of the non-cycloplegic refraction and AL and corneal thickness using swept-source optical coherence tomography (OCT), choroidal thickness using spectral-domain OCT, and tear fluid volume. A questionnaire was completed that included lifestyle, familial history of myopia, time spent on near-vision activities, use of smart devices, and outdoor activities in general.¹³

The primary outcome was the change in the choroidal thickness compared with the baseline value.

The investigators reported, “After 1 week of the camp program, the choroidal thicknesses increased significantly by 30.7 ± 20.3 μm (P < 0.001). The baseline and final choroidal thicknesses were, respectively, 349.0 ± 81.5 μm and 379.7 ± 79.9 μm. The baseline and final values of the central corneal thicknesses, were, respectively, 543.1 ± 39.0 and 545.3 ± 39.3 μm (P = 0.022).”

Ogawa and colleagues concluded, “We conducted eye examinations for schoolchildren in their early teens before and after a 1-week program at a low-altitude mountain summer camp. Our results suggested that participating in the outdoor camp for 6 hours per day for only 1 week increased the choroidal thickness.”

References

1. Ogawa M, Torii H, Yotsukura E, et al. Intensive outdoor activity for 1 week increases choroidal thickness in Japanese schoolchildren: a prospective observational study. BMC Ophthalmology. 2025;25:300. https://doi.org/10.1186/s12886-025-04128-2

2. Holden BA, Fricke TR, Wilson DA, et al. Global prevalence of myopia and high myopia and Temporal trends from 2000 through 2050. Ophthalmology. 2016;123:1036–42.

3. Maruyama T, Yotsukura E, Torii H, et al. Children in Tokyo have a long sustained axial length from age 3 years: The Tokyo Myopia Study. J Clin Med. 2022;11.

4. Karthikeyan SK, Ashwini DL, Priyanka M, Nayak A, Biswas S. Physical activity, time spent outdoors, and near work in relation to myopia prevalence, incidence, and progression: an overview of systematic reviews and meta-analyses. Indian J Ophthalmol. 2022;70:728–39.

5. Biswas S, Muralidharan AR, Betzler BK, et al. A duration-dependent interaction between high-intensity light and unrestricted vision in the drive for myopia control. Invest Ophthalmol Vis Sci. 2023;64:31.

6. Strickland R, Landis EG, Pardue MT. Short-wavelength (violet) light protects mice from myopia through cone signaling. Invest Ophthalmol Vis Sci. 2020;61:13.

7. Biswas S, Busoy JMF, Barathi VA, et al. Interactions between high-intensity light and unrestricted vision in the drive for hyperopia. Invest Ophthalmol Vis Sci. 2024;65:22.

8. Wu PC, Chen CT, Lin KK, et al. Myopia prevention and outdoor light intensity in a school-based cluster randomized trial. Ophthalmology. 2018;125:1239–50.

9. Flores-Moreno I, Lugo F, Duker JS, Ruiz-Moreno JM. The relationship between axial length and choroidal thickness in eyes with high myopia. Am J Ophthalmol. 2013;155:314–e91.

10. Zhang Y, Jeong H, Mori K, et al. Vascular endothelial growth factor from retinal pigment epithelium is essential in choriocapillaris and axial length maintenance. PNAS Nexus. 2022;1:pgac166.

11. Xu M, Yu X, Wan M, et al. Two-year longitudinal change in choroidal and retinal thickness in school-aged myopic children: exploratory analysis of clinical trials for myopia progression. Eye Vis. (Lond). 2022;9:5.

12. Hansen MH, Kessel L, Li XQ, Skovgaard AM, Larsen M, Munch IC. Axial length change and its relationship with baseline choroidal thickness - a five-year longitudinal study in Danish adolescents: the CCC2000 eye study. BMC Ophthalmol. 2020;20:152.

13. Yotsukura E, Torii H, Inokuchi M, et al. Current prevalence of myopia and association of myopia with environmental factors among schoolchildren in Japan. JAMA Ophthalmol. 2019;137:1233–9.