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Dr Andrew Fink MD for
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Eye Clinic,
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Ra'anana, Israel
Towards Healthy eyes-How to Choose the Right Sunglasses
Although our eyes our designed to absorb light enabling us to see, extreme brightness generates an innate protective response. We tend to squint in attempt to reduce the amount of light reaching our eyes. The pupil constricts reducing further light entry and of course we just turn away when it becomes too much. Sunglasses enable us to function better in otherwise difficult conditions. Darkened lenses absorb the unpleasant dazzle and glare of bright sunshine, whilst UV filters protect our eyes’ health from dangerous UV light. Here are some tips on choosing your next pair of sunglasses.
Check the label for 100% UV protection. UV light is absorbed by a substance impregnated within or on the surface of the lens.
The design of the glasses frame is important not just from a fashion point of view. The frame should be closely fitting to the face. Tests on manikins show that even with lenses that block out 100% of UV light, about 14% of UV still reaches the eye around the sides. Moving the glasses 6mm from the face increases UV penetration up to 45%. For this reason large lenses and wrap-around frames are recommended. A wide brimmed hat helps prevent UV entering from above and is especially important in children who refuse to wear glasses.
How dark a lens to choose depends on their usage and personal sensitivity to light. Skiers and sailors subject to much reflected light will want very dark lenses, whilst for daily use in variable lighting conditions lighter lenses will enable greater function. Lenses with graduated tinting, lighter at the bottom, enable drivers to see the dashboard whilst reducing glare from the sky and road ahead.
Grey coloured lenses are popular as they cause least colour distortion. Brown and yellow lenses are most effective in reducing glare enabling clearer vision, but tend to make everything look yellowy.
Other additions such as polarising and reflective coatings all tend to reduce dazzle, but have no effect on UV light absorption, which must always be checked for separately.
Poor quality dark lenses, often just coloured plastic, without UV filters cause more harm than wearing no sunglasses at all. This is because the dark lenses reduce the visible light reaching the eye causing the pupil to dilate somewhat, which consequently enhances the entry of more unfiltered dangerous UV light. Certain designer frames with small lenses and thin side arms are similarly to be avoided.
Don’t be misled by price. Expensive glasses usually indicate fashion trends and durability, not UV protection. However very cheap sunglasses, or toy glasses for children, bought at a market stall for example, may be of dubious quality whatever the label may say.
Contact lenses and implanted lenses after cataract surgery do contain UV filters but not enough, and sunglasses must still be worn.
For more information see: http://travel.howstuffworks.com/sunglass.htm
