The evidentiary basis and challenges associated with studying the role of light damage on ocular health.

The interaction between light and the eye is both essential and potentially harmful. Light regulates ocular development, supports vision, and influences systemic physiology, yet it can also induce photochemical damage. Determining whether chronic exposure to high-energy visible (HEV) light contributes to age-related ocular disease remains challenging. Randomized clinical trials, the gold standard for medical evidence, are largely infeasible for exposures that are lifelong, ubiquitous, and potentially harmful. Instead, researchers rely on a spectrum of evidence, from cellular and animal models to case studies, cohort studies, and expert consensus, each with unique advantages and limitations. This review categorizes existing evidence according to study design, evaluates its strengths and weaknesses, and considers how converging findings might inform clinical practice. We conclude that while acute light injury is well established, the long-term impact of low-level HEV exposure remains largely and necessarily inferential. Definitive evidence is difficult to obtain but improvements in exposure assessment and integration across different categories of evidence have led to a cautious but reasonable conclusion on the potential harms of long-term exposure.