MORE THAN MEETS THE EYE

The sun supports life on our planet, but its life-giving rays also pose hazards. With the constant publicity around the dangers of ultraviolet rays for our skins most of us apply sunscreen with hardly a second thought. What we are generally less aware of is how ultraviolet light from the sun affects our eyes. While the body needs a certain amount of UV light for the production of vitamin D, an excessive amount can be harmful to the skin and eyes. There are three types of ultraviolet (UV) radiation. UV-C is potentially the most dangerous, but almost all of it is blocked by the ozone layer – a situation that may change with ozone depletion, especially in countries like Australia and South Africa. However, UV-A and UV-B radiation can have long- and short-term effects on the eyes and vision. In low doses UV-B rays stimulate the production of melanin resulting in a suntan, but in higher doses they can cause sunburn and premature aging of the skin. UV-A rays have the lowest energy but can pass through the cornea, damaging the lens and the retina. 

If your eyes are exposed to excessive amounts of UV radiation over a short period of time, you may experience photokeratitis. Like a "sunburn of the eye," its symptoms include red eyes, a gritty feeling in the eyes, extreme sensitivity to light and excessive tearing. Fortunately, these symptoms are usually temporary and rarely cause permanent damage to the eyes. The longer the eyes are exposed to solar radiation, the greater the risk of developing cataracts or macular degeneration later in life. UV damage begins in early childhood, is cumulative and irreversible. 

Levels of UV radiation vary, depending on a number of factors. Average UV levels in summer are three times greater than in winter and are most damaging in the middle of the day. UV levels are higher at higher altitudes, greater in tropical areas and lower as one moves further away from the Equator. The risk of UV exposure is lower in urban areas where tall buildings provide shade, and greater in wide open spaces particularly if there are reflective surfaces like expanses of water and sand. In addition certain medications can increase the body's sensitivity to UV radiation. Most important to remember is that UV radiation is present even on cloudy or overcast days. 

Over the years, sunglasses have become a fashion accessory worn to make a statement but let's not forget that their primary function is to protect the eyes. When buying sunglasses how do we know that what we choose will be effective in protecting our eyes? More expensive does not mean more protection and the colour or darkness of the lens does not necessarily indicate the level of sun protection. Most sunglasses today have some UV protection embedded in the lens and most reputable brands list UV protection on their label. Rather than looking at the price tag, look for a label that says "100% protection against both UVA and UVB". The lenses should also be free of distortion and imperfections. Scratches on the lenses will not harm the eyes but looking through a defective lens could cause unnecessary eyestrain. If you spend a lot of time outdoors wrap-around sunglasses will protect the eyes from UV rays coming in from the side, as well as protecting the delicate skin around the eyes. 

One would expect that the darker the lenses are the more protection they offer, but this is not always the case, as the treatment of the lenses determines their level of protection. The colour of the lenses has a role to play in blocking UV radiation. Brown tinted lenses filter blue light best and improve contrast on grass and against the blue sky. Grey and green-grey tinted lenses do not alter the colours of the surroundings, making it easier to estimate distances. Yellow and orange tinted lenses are generally used for specific types of sports glasses. Ultimately, the colour of the lenses is a matter of personal preference. 

In order to minimise glare, sunglasses with anti-reflective and polarised lenses are recommended. Polarisation has nothing to do with UV light absorption, but many polarised lenses are now combined with a UV-blocking substance. As well as the reduction of glare, the benefits of polarised lenses include improved visual comfort, improved visual clarity, reduced eyestrain, reduced reflections and true perception of colours. Photochromic lenses automatically darken in response to UV light, fading back to clear away from UV light. They are convenient in that one doesn't need to keep changing glasses when moving from indoors to outdoors and back again and are a good choice for people who are sensitive to light. 

Thanks to widespread awareness about the dangers of ultraviolet rays, most parents are vigilant about protecting children's skin with sunblock, hats and clothing. But they tend to forget about eye protection. Children spend a lot of time outdoors and their eyes haven't fully developed yet. A child's pupil is larger than an adult pupil, allowing more light to enter the eyes. Added to that, children's eyes do not filter UV radiation as effectively as adults' eyes do. They need sunglasses that protect against UVA and UVB rays, even on overcast days. A wide-brimmed hat is a good idea, but it doesn't replace sunglasses. Reflections from the sun are still getting into their eyes. 

When choosing sunglasses for children, the lenses should be polycarbonate if possible as they are impact-resistant, UV protective and lighter than standard lenses. A large frame always provides the best protection, with temples that are a little wider to prevent peripheral sun from getting in. The frame should be close-fitting and flexible so that they are less likely to break easily. If a child already wears prescription glasses, photochromic lenses that change from light to dark may be a better option than an extra pair of sunglasses. 

When getting children to wear sunglasses, lead by example. If parents are wearing sunglasses and putting a hat on when they go out into the sun, children are more likely to mimic that behaviour. Let the child have input into choosing the glasses, so that they feel committed to wearing them and being responsible about taking care of them. 

There is the misconception that once summer is over the danger of UV damage to the eyes is over too. While it does pose less risk than in summer, the radiation from the winter sun can cause eye damage. Sunglasses are the key to eye protection regardless of the season or the weather.