Chances are: if you are living in the northern hemisphere, your eyes will be exposed to the sun as you stroll out on a summer’s day. If you are a part of the 27% of people who don’t wear eye protection when they are outside, you are risking your eyes to ultraviolet radiation (1). While your body may produce vitamin D from the sun, the production of vitamin D is stimulated by ultraviolet radiation (UVB rays). Ultraviolet radiation comes in three types: UVA, UVB, and UVC. UVC may be harmless because it is absorbed by the atmosphere, but UVA and UVB can damage the skin and eyes (1). The effects of eye exposure to ultraviolet radiation include eye irritation, “trouble seeing”, wrinkles around the eye, red or swollen eyes, sunburned eyelids, and cancer.
Two main effects of ultraviolet radiation exposure involve cataract formation and retinal degeneration (lens and retinal alterations, respectively). The proposed mechanism for these alterations is the generation of oxygen radicals that cause lipid peroxidation and protein modification (2). Lipid peroxidation is the degradation of lipids and similar to protein modification, results in cell damage. Products of lipid peroxidation were found in vitamin E-deficient and supplemented retinal tissue. The oxidized fatty acids alter the permeability cell membranes (phospholipid layers) and lead to cell behavior change or death (2). Vitamin E can inhibit lipid peroxidation but the lack of can also change membrane structure. A product of lipid peroxidation is 4-hydroxyalkenals (aldehyde) which inactivates proteins, causing retinal damage (2). A cataract is an opacity of the lens, clouding the transparent lens of the eye. The lens refracts light for retina focus. Cataract formation can stem from ultraviolet radiation where lipid peroxidation is inhibited by antioxidants that damage the lens with increasing age through depletion or protein modification (2). Influencing antioxidant status could reduce cataract formation. Retinal degradation stems from photochemical damage where the light-sensitive retina is damaged by lipid peroxidation. The structure of the retina include photoreceptors that convert light into electrical signals and the photoreceptor outer segment is a plasma membrane surrounding disc membranes that are lipid bilayers (2). Lipid peroxidation increases with more double bonds and increased light may also trigger photooxidation reactions (2).
While UV protective glasses are recommended to protect against ultraviolet radiation, Dr. Sharon Moalem proposes a theory that wearing UV protective glasses can increase risks of sunburn by prohibiting melanin production because the eye does not detect sunlight (4). The pituitary gland connected to your optic nerve stimulates the production of a melanocyte-stimulating hormone (MSH) that starts the melanocytes producing melanin. The melanocyte-stimulating hormone peptides primarily play in skin darkening (3). MSH peptides differentiate themselves by binding to different melanocortin receptors (MCRs). The melanin absorbs sunlight so the skin becomes darker as it is more exposed. After being secreted by the pituitary gland, MSH flows in the blood and connects to MCRs on melanocytes: pigment-containing cells (3). The MCRs then activate and increase melanin pigment concentrations. In theory, sunlight stimulates MSH production and secretion creating skin darkening in humans and because UV protective glasses prohibits sunlight from reaching the eye, melanin is not produced to protect the skin from sunburns.
Regardless of whether you are protecting your eyes or skin, protective measures against ultraviolet radiation should be taken. The next time you walk into the sun, wear a hat, sunglasses, and/or sunscreen!
(1) Eye Care & Protection. (n.d.). Retrieved from https://thevisioncouncil.org/content/uv-eye-protection
(2) Kuijk, F. J. (1991, December). Effects of Ultraviolet Light on the Eye: Role of Protective Glasses. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1568237/
(3) Pituitary Gland and Pituitary Tumors. (n.d.). Retrieved August 07, 2017, from http://www.aans.org/Patients/Neurosurgical-Conditions-and-Treatments/Pituitary-Gland-and-Pituitary-Tumors
(4) Moalem, S., & Prince, J. (2008). Survival of the sickest: A medical maverick discovers why we need disease. New York: Harper Perennial.