Sunglasses are bought and worn for many reasons. Some people buy sunglasses purely as a fashion accessory while others have special lenses made specifically to suit their vision needs. This article provides information about different parts of the eyes, ultraviolet (UV) radiation, and things to look for when purchasing sunglasses.

Eyes have three natural ways of coping with the sun, but these are not enough

Your eyes have three natural mechanisms for coping with the sun. First, your eyelids act like blinds on a window to shut out light at will. The eyes' pupils are your second natural mechanism. Pupils work like a camera aperture, adjusting, opening and closing according to the intensity of light they are exposed to. And third, the retinas at the back of the eyes adapt to different brightness levels.

All three natural mechanisms (your eyelids, pupils and retinas) respond quickly to variations in visible light, but they cannot completely keep out UV radiation (which is invisible).

UV radiation can be damaging to healthy eyes if exposure is excessive. Excessive exposure to UV radiation (which causes sunburn) can result in snow blindness, and in the longer term may lead to cataracts, macular degeneration and premature ageing changes in general.

Can you minimise your eyes' exposure to UV radiation?

The right sunglasses will protect your eyes from harmful UV. However, a coloured lens does not necessarily reduce UV absorption - sometimes it will only reduce the amount of light you see. It is important to make sure your sunglasses not only reduce brightness but also protect your eyes from harmful UV radiation.

What should you look for when choosing sunglasses?

The most important aspect of any sunglasses is the lens quality. Lenses come in a huge variety of tints, and can be made of glass, various plastics, or polycarbonate. Sunglasses should conform to the revised 2003 Australia/New Zealand Standard AS/NZS1067.

Glass lenses are generally more resistant to scratching. However, they are more easily broken than plastic lenses, and this carries with it a safety risk when playing sports and the like. They are also likely to be heavier and therefore potentially less comfortable. High quality glass lenses are excellent at selectively absorbing undesirable rays and are available in fixed (solid) or photochromic (light sensitive) tints.

Resin (plastic) lenses are safer than glass as they do not shatter so easily. Often they feature a scratch-resistant hard coating and this helps to ensure a long life. Without such a coating they can become scratched if not properly cared for. Plastics are as optically correct as glass and are lighter in weight. Tints available include solid, graduated polarised or photochromic forms.

Polycarbonate lenses are stronger still and are a must for eye safety when playing sports such as cricket. They offer the ultimate in eye protection and safety, and again the range of tints is extensive.

Most of the options mentioned are also available as prescription lenses. An optometrist can discuss the huge range of options available, to ensure your requirements are met.

What about the colour of the lenses?

Different lens colours and treatments provide differing levels of protection against UV radiation. Brown or amber lenses are good for absorbing UV light and blue light. This can serve to enhance contrast. Grey lenses do not distort colours while polarised lenses absorb reflected light.

No sunglass lens is ever dark enough to observe the sun or eclipses. Never ever look directly at the sun or an eclipse. This could result in your permanent loss of vision. However, sunglasses do make it difficult to see well in poor light conditions so dark lenses should never be worn while driving at night.

What about the frames?

You must also think about your frames. As with spectacles, there is a wide range of frames available. When choosing frames, your optometrist will provide you with specific information about your needs. We suggest your sunglass frames should be comfortable, serviceable and perhaps fashionable. Close-fitting, wrap-around styles offer better protection for not only the eye itself, but also for the eyelids and surrounding tissues. For certain situations wrap-around frames can be fitted with tinted prescription lenses although these would have to be specially made and hence a little more expensive than standard options.

Plastic sunglass frames are generally strong and durable. Some plastic frames are mass-produced and as such, do not allow for individual facial differences. Consequently, they may not be adjustable. We recommend you take time to ensure plastic frames fit well particularly on your nose. This is so they are comfortable to wear.

Metal sunglass frames are usually adjustable. They often have more moving parts that will require maintenance. Cheaply made metal frames may use brittle metal and, as a result, are less durable.

Do children need sunglasses?

Children need to wear sunglasses as much as adults do because their eyes need protection from UV radiation. Also, children may spend many hours in the sun and they often have larger pupils that let more light enter the eye.

Some final words of advice

Although price is important for everyone, it is important to think of aspects such as value for money and how long your sunglasses will last. Remember, you only have one set of eyes and because of this, protection from damaging UV and infrared rays ought to be a priority.

To ensure your sunglasses last as long a possible, it is recommend storing them in a case that provides strong protection. These are available from your optometrist.

Ultimately, you should to feel good about wearing your sunglasses. Remember, they are important because they provide additional protection for your eyes against damaging UV radiation.

Your optometrist can provide you with sunglasses and vision information tailored to your individual needs. You should ask any questions you may have, take your time when choosing from the range of options, and be careful in the care and maintenance of your new sunglasses. That way, you should feel safe in the knowledge you are protecting your eyes in the best possible way.

To find details of your nearest optometrist check the New Zealand Association of Optometrists website www.nzao.co.nz or phone 0800 439 322.

Original material provided by the New Zealand Association of Optometrists, updated by everybody February 2008.