The sun is a large body which emits harmful short-wavelength ultraviolet radiation. This, in turn, is absorbed by the ozone layer in the stratosphere. Unfortunately, the protection afforded by the ozone layer is being reduced by the use of chlorofluorocarbons (CFCs) which break down the ozone molecules.

In the human body, harmful free radicals are formed as a by-product of the process that converts food into energy. They are mopped up by antioxidants (principally Vitamins A, C, E, and beta-carotene) which help counter the cell damage to the eyes associated with free radical activity.

Ultraviolet radiation could be described as solar "free radicals". As it is wise to limit free radical damage to the eyes by eating an antioxidant-rich diet, so it is sensible to take precautionary measures to guard against solar "free radicals" or ultraviolet radiation.

How hazardous is this solar radiation to our vision? Most of us are familiar by now with its associated risks of skin cancer, but it also contributes to various types of damage to the eyes (e.g. snow blindness or photokeratitis, and various opacities on and within the eyes, including fat deposits and cataract).

Although there is little evidence that ultraviolet levels have increased substantially in non-polar regions of the world, the breakdown of the ozone molecules by man-made chemicals does continue apace. It is wise, therefore, to put yourself on vision care alert on sunny days.

Amounts of potentially damaging ultraviolet radiation have always been at their highest around noon local-time at the height of summer. These harmful rays also increase the nearer you move to the equator and the higher the altitude reached.

Sand and snow reflect large amounts of ultraviolet radiation. Skiing or other activities on snow (especially during summer) certainly requires you to wear adequate protection for your eyes. Similarly, bathing on beaches near the equator increases the risk of damage to your vision and cells for category 2 (20% transmittance) sunglasses.

Besides sunglasses, a broad-brimmed hat reduces considerably the amount of light striking the eyes when walking or standing. Although, as we have seen, good quality sunglasses provide the best protection against ultraviolet radiation, ordinary clear plastic or high-index glass lenses also provide considerable protection as well.

It is important to remember that ultraviolet rays do not just come from above. Ambient ultraviolet radiation can also come from the side or be reflected from below. So, protection against ambient ultraviolet is desirable, and care should be taken when buying the currently fashionable small-sized frames to check that these also give adequate protection from above.

Everyone can benefit from improved ocular comfort in bright, sunny conditions, but are they really necessary when skies are cloudy? You might be surprised to learn that many types of cloud have only a small effect on the levels of ultraviolet reaching the ground. It is, then, only sensible to continue to protect the eyes in high-risk environments even when it is cloudy.

As exposure of the skin to too much short wavelength ultraviolet radiation can lead to skin cancer, so exposure of the eyes to excessive ultraviolet radiation can lead long-term to

serious eye disease.

A few hours after excessive exposure your eyes will become very red and watery. They might feel "gritty" and even natural light, not strong sunlight, can be painful to the eyes. A period spent in a darkened room may feel more comfortable.

Fortunately, this short-term photokeratitis will begin to subside within 24 hours or so and usually disappears completely after 48 hours. However, as with red, burnt skin so with red "burnt" eyes: the redness indicates potential long-term damage and it is always preferable to avoid the damage in the first place.

It makes sense, then given the ongoing depletion of the ozone layer, to take seriously the damage caused by these solar "free radicals". Be wise: maintain a high vision care alert!