Evaluation of solar ultraviolet blocking by sunglasses and their compliance with recommended safety limits

Solar ultraviolet (UV) radiation upon the eyes is related to many ocular diseases and sunglasses play an important role in preventing eye injuries. The World Health Organization and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) have established safety limits on the exposure of eyes to UV radiation, which are, for an 8-h period under the sun: 1) UV radiant exposure should not exceed 30 J/m² when irradiance is spectrally weighted using an actinic action spectrum; and 2) unweighted radiant exposure in the UV-A region should not exceed 10 kJ/m². This study investigated whether sunglasses truly prevent the incoming of UV energy on the eye surface, restraining it below the recommended limits. This study was performed before and after artificial aging of the lenses in a solar simulator.

The solar spectral irradiance was modeled using an open source spectral model, in which a clear sky condition have been assumed, aside from information about site location, date, time, ozone column, aerosols, and turbidity. In addition, the spectral transmittance of 12 typical sunglasses lenses was measured and the global solar irradiance was weighted with the spectral transmittance profile for each lens. Then, the UV and UV-A radiant exposure incident upon the eye through the lenses were calculated for each day of the year, before and after the aging process, for comparison.

The findings showed that most sunglasses fail to meet at least one of the two ICNIRP safety limits. One lens revealed itself to be optimal because it completely blocked the UV radiation, even after undergoing the aging test. This particular lens contains a UV filter that adheres to both ICNIRP safety limits.

The majority of sunglass lenses in this study inadequately filtered harmful UV radiation, leaving eyes susceptible to long-term injury. To ensure effective vision protection, the sunglass industry should adopt the ICNIRP safety limits as a standard practice. This would enhance product quality and guarantee comprehensive UV protection for the eyes.