The impact of light properties on ocular growth and myopia development

The objective of this article is to comprehensively review the effect of environmental lighting on ocular growth and refractive status in both animal and clinical studies, with an emphasis on the underlying mechanisms. This review was performed by searching research articles and reviews utilizing the terms "myopia," "light therapy," "axial length," "refractive error," and "emmetropization" in PubMed datasets. The review was finalized in December 2023. In the animal studies, high lighting brightness, illumination periods aligning with circadian rhythm, and color contrast signals including multiple wavelengths all help regulate ocular growth against myopia. Long wavelengths have been found to induce myopia in chicks, mice, fish, and guinea pigs, whereas shorter wavelengths lead to hyperopia. In contrast, red light has been observed to have a protective effect against myopia in tree shrews and rhesus monkeys. Apart from wavelength, flicker status also showed inconsistent effects on ocular growth, which could be attributed to differences in ocular refractive status, evolutionary disparities in retinal cone cells across species, and the selection of myopia induction models in experiments. In the clinical studies, current evidence suggests a control effect with red light therapy. Although the lighting conditions diverge from those in animal experiments, further reports are needed to assess the long-term effects. In conclusion, this review encompasses research related to the impact of light exposure on myopia and further explores the retinoscleral signaling pathway in refractive development. The aim is to establish a theoretical foundation for optimizing environmental factors in lighting design to address the epidemic of childhood myopia.