We usually associate sunglasses with long hot summer days, time at the beach or pool, iced drinks, and protecting our skins from the sun's harmful rays. Before you put away your sunglasses along with your sun screen until next summer, remember that sunglasses are not simply a summer item, but play a vital role in eye care, even in winter.

TV and magazines are full of fashion eyewear and facts about the danger of UV rays to the eyes in summer, but they tend to neglect the fact that the sun still shines in winter. Although the winter sun is less intense than it is in summer and the UV rays are weaker, the winter sun can still damage the eyes. Being lower in the sky and at a different angle, it often shines directly into the eyes.

The tissue that makes up the human eye is some of the most sensitive and vulnerable tissue in the body. The eye has many natural defenses that protect it from the sun's rays, including pupil dilation, the squinting reflex, and the concave shape of the eye socket, shielded by the brow. However, the eyes' natural defenses are not adequate in protecting them from all harmful UV radiation. Reflexes like squinting and pupil dilation are only triggered by the sun's visible light. That means that on cloudy days, the amount of UV light reaching the unguarded eye can be dangerous.

Two different types of light enter the eye, namely ultra violet (UV) light and visible light. UV light cannot be seen by the naked eye whereas visible light can be seen. When visible light penetrates the eye, it falls on the retina at the back of the eye, and an image is produced. Visible light is minimised on cloudy days but the exposure to UV rays is still high. While the body needs a certain amount of UV light for vitamin D production, an excessive amount can be harmful to the skin and the eyes. The damage to the eyes from UV light accumulates over time, and eye conditions resulting from this develop gradually over time. High altitudes increase radiation, and certain medications make the eyes more sensitive to its effects.

There are three types of UV rays, A, B and C. The lens of the eye absorbs UVA light to help protect the retina. Continuous long-term absorption of UVA light leads to degenerative changes within the lens and the possible development of cataracts. Macular degeneration, too, has been linked to over-exposure of the eyes to UVA light. UVB light causes sunburn and so-called ‘snow blindness' from reflections off water, sand and snow. The cornea protects the eye against UVB rays, but the conjunctiva (the mucous membrane that covers the front of the eye and lines the inside of the eyelids) remains exposed. UVB radiation can lead to the development of pterygiums and pingueclas. These are little white elevated tissue growths on the conjunctiva. Although not sight threatening, they can become uncomfortable, red and unsightly when exposed to the elements. UVC is absorbed by the ozone layer and has the highest energy UV rays, which make them the most harmful to the eyes.

With higher levels of UV radiation reaching the earth's surface, it is important that people take the proper steps to protect their eyes. Not all sunglasses give adequate protection for the eyes, so make sure that the ones you choose block out 99 – 100 % of both UVA and UVB radiation. Wrap around frames protect the eyes from every angle, and shield the delicate skin around the eyes. Brown-tinted lenses provide the best protection against UV and visible light, and do not distort colours. On the beach or near water, glare protection is important, and even in the shade the eyes need to be shielded from reflections. Sunglasses should be worn on overcast days when visible light may be low, but UV radiation is high.

Clear prescription glasses offer some UV protection, but UV coating on the lenses would obviously be more effective. Talk to your optometrist about the most effective lens material for UV protection, as well as anti-reflective and polarized coatings. Photochromic lenses are activated by UV light, and not visible light, so that the darkening depends on temperature and sunlight. If you wear contact lenses, discuss with your optometrist wearing lenses that provide extra UV protection, but you will still need to wear sunglasses for better protection as the lenses do not cover the whole eye, and the skin around the eyes is still exposed. If you use tanning beds, be sure to wear eye protection, as the eyelids are thin and the high levels of UV radiation can reach the eyes even if they are closed.

Children are also in need of UV protection. They spend a lot of time outside and are at risk of potential damage to their eyes and skin. Provide them with good quality sunglasses and encourage them to wear brimmed hats on sunny days. Set a good example by wearing sunglasses yourself.