We’ve all heard about the importance of wearing hats and using sunscreen to protect our skin from the harmful effects of UV radiation. But how can we protect our eyes? Sunglasses offer some of the best ocular protection from UV light but blocking the harmful rays from reaching the delicate tissue of our eyes. Most sunglasses block (category 2 and 3) block more than 95% of UV radiation. Keep in mind that the colour or the darkness of the lens tint does not indicate how much UV is blocked so always check the tag/label to determine the level of protection.
Some prescription spectacle lenses also block UV light. At Gerry & Johnson Optometrists, all of our prescription lenses block 100% of both UVA and UVB light to protect our eyes from the early development of eye disease. The UV protective treatments are applied on the front and back surface of the lens, as around half of UV light entering the eye is reflected from the back surface of the lens.
Some contact lenses also offer UV protection. Although sunglasses can efficiently block the UV radiation coming directly from the sun, they may fall short elsewhere. Unless the frame is designed to wrap the face like a pair of goggles, sunglasses block very little of the obliquely incident UV radiation (as seen in the figure below). Peripheral UV radiation has been shown to be a particular threat to eye health due to the phenomenon of peripheral light focussing (PLF), where oblique light is refracted by the peripheral cornea and focused at the nasal limbus (white part of the eye towards the nose).
PLF has been shown to play a significant role in the development of pterygium and some forms of cataract. Since soft contact lenses cover the cornea and land just past the limbus on the white of the eye, they are able to protect the eye more completely. Also, as contact lenses are worn generally for significantly longer periods of time than sunglasses, they are able to provide continuous protection against UV.
The benefits of UV light
At the risk of confusing the issue, did you know that UV light is not all bad!? In small amounts, UV radiation is actually a benefit to the human body. UV radiation is required for the synthesis of vitamin D which is needed for the growth and maintenance of strong healthy bones. UV light has also been shown to be beneficial for the eyes as research shows that it has a myopia control effect. Myopia, or short-sightedness, is fast becoming one of the major vision problems around the world. Even small degrees of myopia significantly increase a person’s risk of eye health complications such as glaucoma, cataract and retinal detachment. Research suggests that the protective effect of UV radiation involves the light-dependent release of dopamine in the retina. Dopamine has been shown to inhibit axial elongation (increases in eye length) which leads to myopia development and also progression. The amount of UVR required for good health is easily gained by spending approximately ten minutes outside each day in ambient light. So for any outdoor activities, especially over the summer (think the beach, pool and shopping days!) remember to wear protective eyewear and clothing!
If you haven’t already, check out last week’s blog on the known health effects of UV!
Bergmanson, P.G., Sӧderber, P.G. The significance of ultraviolet radiation for eye diseases. A review with comments on the efficacy of UV-blocking contact lenses. Ophthalmic Phys Optics. 2002; 15(2): 83-91.
Sliney, D.H. Photoprotection of the eye – UV radiation and sunglasses. J Photochem Photobiol B: Biol. 2001; 64(2-3); 166-175.