A 2024 study from São Paulo, Brazil, has revealed sunglasses with poor UV protection can be more harmful to your eyes than not wearing any at all due to increased field of view (FOV) rather than to pupil dilation. The finding debunks a popular patient belief that sunglasses lacking adequate UV protection exacerbate ocular damage by increasing pupil dilation, allowing more harmful UV to reach the retina, despite no existing literature supporting this theory.

This new open access study, published in Scientific Reports, found a wider FOV in bright environments was the main culprit for increased UV exposure. Out of 214 lenses tested, varying from category 1 (lightest tint) to category 4 (darkest tint) and including non-category lenses exceeding the ISO darkness standard, eight posed higher risks when worn compared with no protection. Categories 2 and 3 lenses with less than 86% UVA protection were particularly hazardous to the eye as they allow more UV influx than if the sunglasses had not been used, reported researchers, while higher category 4 and non-category lenses were safe due to sufficient UVA protection. UVB protection had negligible impact, they said.

The study revealed FOV's impact on UV influx is up to 314.3% greater than the pupil size's contribution. This revelation has significant implications for sunglasses standards, said researchers, and manufacturers should aim for UV400 protection to prevent unnecessary UV exposure and enhance safety. “Our results support the main conclusion that wearing sunglasses with poor UV protection may worsen the hazards to interior eye health.”