Visual environmental risk factors in outdoor activities and near work and potential mechanisms.

Purpose: Myopia is highly prevalent among children and adolescents and results from abnormal refractive development. Less outdoor time as well as more near work have been recognised as major risk factors for myopia. This study analysed the major environmental factors related to myopia, such as outdoor activities and near work, and reviewed the potential mechanisms of myopia development.

Methods: A systematic search was conducted across PubMed, Web of Science, Cochrane Library and Ovid databases within the last two decades up to November 2024. This review followed the recommendations of the PRISMA Statement and only full-text review articles in English were included.

Results: Summarising the findings from 13 review articles, the environmental risk factors for myopia included lighting features such as low illumination and monochromatic light as well as aspects of the visual scene, for example, the presence of low spatial frequencies and hyperopic defocus. These particular visual stimuli may contribute to the onset and progression of myopia and increase the risk of retinal disorders by reducing choroidal blood flow, leading to scleral hypoxia and remodelling. When analysing environmental risk factors, it is challenging to isolate the individual contributions of outdoor time and near work. Furthermore, previous studies used different definitions of environmental exposures.

Conclusions: Future research needs quantitative, objective and standardised measures to improve the comparability and consistency between studies. In addition, work should focus on different ethnic populations and gene-environment studies, so as to determine the influence of environmental risk factors on myopia.