Although the risks of excess solar ultraviolet (UV) exposure of the skin are well recognized, the need for eye protection is frequently overlooked, or when sunglasses are also recommended, specific guidance is wrong or is not explained. Guidance from the World Health Organization at its InterSun webpage advises people to wear “wrap-around” sunglasses under many conditions. The objective of this study was to examine the need for UV filtration in prescription lenses, contact lenses, and sunglasses.
The geometry of UV exposure of both eyes, solar position, ground reflection, pupil size, and lid opening were studied. Because an accurate determination of cumulative ocular exposure is difficult, the cornea itself can serve as a biologic dosimeter, because photokeratitis is not experienced on a daily basis but does under certain ground-surface and sunlight conditions. From a knowledge of the UV-threshold dose required to produce photokeratitis, we have an upper level of routine ocular exposure to ambient UV.
From ambient UV measurements and observed photokeratitis, the upper limits of UV exposure of the crystalline lens or an intraocular lens implant are estimated. The risk of excess UV exposure of the germinative cells of the lens is greatest from the side. Sunglasses can actually increase UV exposure of the germinative region of the crystalline lens and the corneal limbus by disabling the eyes' natural protective mechanisms of lid closure and pupil constriction! The level of UV-A risk is difficult to define.
Proper UV-absorbing contact lenses offer the best mode for filtering needless exposure of UV radiation of the lens and limbus.
Presented at the CLAO UV Radiation Symposium, Las Vegas, NV, September 26, 2010.
Dr. Sliney is a Medical Physicist, Fallston, MD, who retired from the US Army Medical Department, and was the former Chair, ICNIRP SC-IV—Optical Radiation and a past Division Director (Photobiology and Photochemistry) of the International Commission on Illumination (CIE).
The author has no funding or conflicts of interest to disclose.
Address correspondence and reprint requests to Dr. David H. Sliney, Ph.D., Consulting Medical Physicist, 406 Streamside Drive, Fallston 21047-2806, MD; e-mail: email@example.com
Accepted April 23, 2011.