The sun produces infrared, visible and ultraviolet light. UV is made up of blue short wavelength light that is invisible to us. It is divided into three wavelength measurements – UVA 320-400nm, UVB 290-320nm and UVC 100-290nm.
UVA is the main cause of serious skin damage as it can penetrate deeply, pass through clouds, water and glass and is constantly present daily, all year round.
UVB is responsible for surface skin damage and causes sunburn. It cannot pass through glass and is strongest in the summer months between 10am and 2pm.
UVC is highly dangerous and is absorbed by the ozone layer so does not reach us.
We all know that exposure to UV radiation is likely to cause skin damage but few are aware that the eye is also at risk. UV may have some benefits, such as formation of Vitamin D, when absorbed by the skin, but it will only cause damage to the eyes.
UV exposure can lead to several eye conditions including the development of cataracts and macular degeneration. UVB is filtered by the cornea and does not reach the eye lens or retina but UVA is absorbed by the lens and some may reach the retina. The risk of damage can be greatly reduced by wearing sunglasses and a wide brim hat. It is also important to be aware that the risk of UV radiation is not only high from direct sunlight but can also be a problem when light is reflected from surfaces such as snow, buildings and water, and on an overcast day where the clouds are high.
Bright light conditions, such as strong sunlight, may lead to discomfort due to glare. The eye pupil is designed to constrict to protect the eye but in extreme conditions may not shrink enough. This may lead us to ‘screw up’ our eyes to compensate, which in turn may cause headaches through muscle strain. Many suffer from a condition called photophobia where the eyes are especially sensitive to light and may benefit from tinted lenses even when the light level is low.
All types of glasses will act as a physical barrier, shielding the eyes from the wind and airborne particles. People prone to dry eyes and contact lens wearers often benefit from this form of protection as wind will cause faster tear layer evaporation causing increased dryness and discomfort. Hay fever sufferers may also find that sunglasses offer some relief by stopping pollen from entering the eye. Dusty conditions can be problematic and glasses will help to limit dust and dirt avoiding painful corneal abrasions. In all cases a large, close fitting style would provide the best cover.
Children are likely to spend more time outdoors and have more exposure to reflected surfaces such as pavements and sand, yet they are less likely to wear eye protection. They also have larger pupils and the young eye lens is clearer allowing more UV light into the eye. Studies have shown that a person gets a huge chunk of their lifetime UV dose by the age of 18 and this becomes more significant with longer life expectancies. Sunhats are a must have for this age group and sunglasses should be worn in bright sunshine. It is not advisable for children to wear sunglasses all of the time as this will cause the pupils to remain unnaturally dilated for too long. A medium tint is generally recommended and this is because a light tint won’t offer sufficient glare reduction and a dark tint will encourage excessive pupil expansion.
Just because the price tag is low does not mean that all cheap sunglasses are of poor quality. UV protection is the one thing that sunglasses must provide because without it, tinted lenses will cause the eye pupil to dilate, which will allow more UV radiation into the eye. The most important thing to look for when buying any sunglasses is either a CE mark, which is the European standard of UV protection, or a UV 400 label, both of which will ensure that the damaging UVA rays will be blocked.
Some of the very low priced sunglasses have lenses that are cut out of a large sheet of plastic and may cause significant visual distortion and eyestrain. Good quality lenses are glazed individually to ensure optical clarity.
The cheapest frames are often made out of inferior material that cannot be adjusted to allow for a good fit.
Beware of cheap designer sunglasses – they may be fake and may not provide adequate UV absorption. Make sure that you source your sunnies from an authorised retailer.
Most sunglass lenses are tinted brown or grey and the colour chosen is down to personal choice. Some manufacturers, such as Oakley and Dirty Dog, specialise in eyewear for different sporting or environmental requirements and will offer a range of tint options to suit. Here are some colour-related benefits:-
Grey or Grey-Green are the most common lens tints. They allow all colours through the lens without distorting the value of the colours. Dark grey tints are good for bright light situations, as with water sports, because they block out the brightest of the sun’s rays.
Brown coatings give a warmer, slightly brighter lens than grey. They are especially good for blocking the blue diffused light that may be experienced on a cloudy day. They can improve depth perception, contrast and reduce glare and are a good choice in areas of changeable weather.
Yellow will give improved contrast in hazy and foggy conditions by filtering out blue light for sharper vision. Good for low light levels such as at dusk and dawn.
Blue or Purple will lessen glare and enhance colour perception and work well in misty and snowy environments. Blue lenses are currently a popular trend with many designer labels.
Pink or red aid depth perception and contrast and they also reduce eye fatigue.
DEPTH OF TINT
The darkness of a tint can be described in several different ways and this can lead to confusion;
- ABSORPTION – this is the amount of light absorbed by the lens. For example 15% absorption indicates a light tint, 50% a medium tint and 85% a dark tint
- TRANSMISSION (LTF: Light Transmission Factor) – this is the opposite of absorption and is the amount of light that will pass through the lens. For example 15% transmission means a dark tint, 50% a medium tint and 85% a light tint
- 0 to 4 category – with 0 being the lightest, 2 medium and 4 the darkest
- The easiest method is by simply stating light, medium or dark!
The depth of tint is often a personal preference but some conditions will dictate what is advisable. Here are a few recommendations:-
Dark tints are suitable for sunglasses. They are light enough not to impair vision, yet dark enough to provide overall protection from glare on a bright, sunny day.
Medium tints are suggested for those who suffer from glare even when the sunlight is not intense. They can be worn throughout the day.
Light tints are advised for those affected by indoor artificial lights. They lessen the glare from overhead lights. They can also be used on an overcast day for those who are light sensitive.
POLARISED, PHOTOCHROMIC OR MIRRORED?
Polarised lenses are recommended for conditions where light reflection from a flat, horizontal surface, such as water or snow, is a problem and are good for sailing, skiing, driving and fishing. The coating only allows vertical light waves through the lens and the glare-inducing horizontal light is absorbed. Polarised lenses may cause problems when viewing mobile phones or GPS devices as they can make it difficult to view LCD (liquid crystal display) screens. They are not advised for pilots or operators of heavy equipment due to the risk of poor visibility of the control panels.
Photochromic lenses react when exposed to the UV rays from the sun, darkening in bright, sunny conditions and becoming clearer when there is less sunlight. Some people find them convenient as they reduce the need to switch from clear glasses to sunglasses. However most options do not react well behind a car windscreen and are not recommended for night driving as they retain a residual tint. This lens type might also be called light-adaptive or reactolite.
Mirror coatings will also reduce the glare experienced in bright conditions by reflecting light away and will maintain overall contrast.
Tinted prescription lenses are available in a range of options including photochromic and polarised which both come with UV protection. Regular plastic spectacle lenses block UV light up to 350nm, but adding a tint will not provide 100% UV protection and a UV-blocking dye must be added to provide this. Most high-index plastics have 100% UV protection built-in, so an extra lens treatment is not required for these lenses.
Any prescription frame can be used to make sunglasses but it is best to ask for advice if you want to glaze a sunglasses frame as many are not suitable for prescription lenses. Some brands, including Oakley and Maui Jim offer prescription options on certain models.
Sunglasses are commonly only thought of as a stylish fashion accessory and it is nice to know that something that is actually necessary and healthy for us can look so great and make us feel good.
Each year we wait for the top designer labels to launch their new collections to see what the latest novelty will be. Over the last few years we have been through oversized shapes in traditional blacks and browns as well as daring, vivid colours to smaller, round metal styles with bright mirrored lenses in greens, oranges and pinks.
The ever-popular geeky wayfarers are forever being re-invented and this year sees matte frames alongside the familiar shiny frames and vibrant mirrored lens choices spanning the spectrum. Large is still very much out there with striking, angular shapes including the enduring, vintage cats eye.
The standout newcomer this year embraces a subtle round outline and has appeared in many of the top collections. It often features the current craze of fusing metal with plastic but the innovative designers have also used it to soften the contours of bold, chunky shapes and some models incorporate the distinctive, trendy keyhole bridge.
Sunglasses must be one of the most essential yet exciting accessories to own.