UV rays
They are a part of the invisible spectrum of light with a wave length below that of visible light. These rays are invisible and has no relation with the heat of the sun, thus the winter sun has equal amount of UV rays as the summer sun. These rays are divided into UV-A, UV-B and UV-C. UV A and B are known to be the harmful ones. The sunglasses should thus protect from both these rays. There is some evidence to believe that long term UV (UV-A) exposure has a role in cataract formation which is the clouding of the lens. Also UV rays have been held responsible to cause age related macular degeneration (ARMD) which is potentially blinding retinal condition due to old age. Both these conditions can lead to reduced vision. Apart from the above conditions UV exposure can also cause a pterygium which is an over growth of the conjunctiva (skin of the eye). UV rays (UV-B) are also known to cause skin cancers which often occur on the face near the eyes. All of these conditions can be delayed or even prevented by good UV protection of the eyes.
Options in sunglasses
UV protection: Glasses need to have a special coating on it to be able to block the UV rays from passing through. Glasses may have different levels of UV protection, the recommended level is the maximum i.e. 99 to 100% of UV protection of both UV-A and UV-B rays.
Polarized glasses: These glasses have special lenses that reduce glare. They are usually expensive and would help reduce glare directly from the sun or reflected from the road, sand, water or snow. This is independent of UV protection.
Photochromatic glasses: These lenses have the property of changing the darkness of tint depending on the amount of light exposure. They are dark in the sun and automatically become light coloured once taken indoors. This again is independent of UV protection.
Gradient glasses: These glasses are dark in the upper part and become lighter in the lower half of the lens. This is useful while driving to see the dash board through the lighter part.
Tints: There are a number of coloured tints available eg black, brown, grey, blue. This is a personal choice.
Myths
There are a lot of misconceptions regarding sunglasses. Doctors at
Hinduja Hospital try to clarify a few.The common myths while getting a pair of sunglasses is that a darker or more expensive pair of glasses will give good protection. Darkness has nothing to do with UV protection, in fact it is more harmful to wear dark sunglasses without UV protection than not to wear sunglasses at all. This is because behind dark glasses the size of the pupil becomes larger and without UV coating allowing more harmful UV rays to enter the eye which would have otherwise been partially blocked due to a smaller pupil without any glasses. Also most people believe that sunglasses are meant only for the summer months, which is untrue since the UV rays are almost equally harmful all the year round.
Recommendations
You will find many brands & lots of stuff as in sunglasses, but the most recommended by
doctors are the following.
Sunglasses should have a 99 to 100% protection from UV rays (both UV-A and UV-B). Most branded sunglasses will have this information with the product. Some brands have UV 400 written in them which means, it blocks up to 400 nm of light which includes the UV rays.
In case one needs to get prescription sunglasses from the opticians then the amount of UV protection on any lens can be measured by a machine that most good opticians possess.
Since UV damage is long term, starting early is recommended. Children should wear sunglasses whilst outdoors in direct sunlight whenever possible. Very few brands make sunglasses for children and since it is usually difficult to get young children to keep glasses on, a rimmed hat or a cap can usually provide substantial protection.
