Development of a Sun Protection Factor for contact lenses (CL-SPF)

Abstract

Objective Sun Protection Factor (SPF) of sunscreen products is well recognised by consumers. This study explored how SPF could be applied to ultraviolet radiation (UV) protection from contact lenses (CL-SPF). Methods and analysis UV transmission through 15 commercially available contact lenses and three spectacle lens materials was measured with a deuterium light source and spectrophotometer. CL-SPF values were calculated using the standard in vitro method used to test and label skin products. Ray tracing was applied to two sunglass designs to assess the effect of solar angle and head orientation on light reaching the ocular surface. Cellular damage profile of human corneal and conjunctival cells across the UV range was assessed in vitro to inform an SPF equivalent for CLs. Results CLs tested fell into three categories: CL-SPF with no UV blocker=1.0–2.0 (equivalent to using no sunscreen); CL-SPF with Class 2 UV blocker=12.3–24.8 (equivalent to SPF15); and CL-SPF with Class 1 UV blocker=59.6–66.2 (equivalent to SPF 50+). Despite the UV-blocking characteristics of sunglasses, ocular surface protection can be substantially reduced at certain solar angle and head orientation combinations; on average, 76%–89% of light was prevented from reaching the ocular surface depending on the intensity of the tint (80%–20% transmission). The data also suggest that cell damage and death of ocular surface cells has a similar profile to that of the skin, but conjunctival cells are more susceptible to UV damage. Conclusion CL-SPF is a viable metric to communicate the protection from the absorption/transmission of UV radiation that CLs offers wearers. However, a contact lens will only project the area of the ocular surface it covers, which is limited to mainly the cornea and internal eye tissues with soft CLs.