IMI: The Role of Light in Refractive Development and Myopia: Evidence from Animal and Human Studies

Spending time outdoors is consistently associated with delayed myopia onset in children and has been incorporated into prevention programs. While the underlying mechanisms remain under investigation, substantial evidence supports sunlight exposure as a key contributing factor. This review evaluates the evidence supporting this association. Animal studies demonstrate that light characteristics-such as intensity, chromaticity, and photoperiod-can influence refractive development, often postulated to function through modulation of the dopaminergic system. However, translating these findings to humans is challenging due to limited data. Evidence remains insufficient regarding how specific light properties-including intensity thresholds, exposure durations, spectral composition, and temporal patterns-affect human myopia. Consequently, although clinical recommendations for outdoor time (e.g., 2 hours daily) are well supported by epidemiological studies and widely endorsed, current literature does not yet support evidence-based guidelines concerning specific characteristics of light exposure. Addressing this gap requires further randomized controlled trials using standardized wearable technologies to better quantify children's visual environments and identify light-related cues relevant to myopia development. Interest in light-based therapies is growing, but most interventions remain in early stages of development/testing. Due to limited efficacy data or unresolved safety concerns, no clinical recommendations can currently be made. Interpreting light-related research-especially from across animal models-requires caution. Species-specific differences in ocular transmittance and opsin distribution/tuning complicate the translation of chromatically related findings between species and to humans. Moreover, the term "white light" can be misleading, as artificial sources vary spectrally from each other and from sunlight, resulting in varied patterns of opsin activation. Studies should therefore attempt to report not only light intensity, but also the radiant power emitted at each wavelength to enable meaningful comparisons.