The following article was originally written by Susan Blakeney, Glaucoma UK Trustee, for Insight magazine.
As an optometrist, my patients often ask me what the best types of sunglasses to buy are, and whether the price reflects the quality of protection that they offer. The short answer is that price is not necessarily a guide to lens quality and safety. As for the longer answer, here goes….
Sunglasses mainly have two purposes. The first is to protect us from the uncomfortable or dazzling glare of bright light. Normally this is sunlight, but some artificial light can be uncomfortably dazzling too (I would like to mention here that you should never be tempted to wear sunglasses when driving at night if you find oncoming headlights dazzling).
Secondly, they protect our eyes and the skin around them from the damaging effects of sunshine, namely the ultra-violet (UV) part of the spectrum. It is this end of the spectrum which has more energy and can cause damage to our bodies, including our eyes. We can’t see UV light, and we can’t tell whether a lens absorbs UV light simply by looking at it. So we need to rely on the manufacturer’s assurance that a lens (of whatever colour) absorbs safe amounts of it.
To understand the impact of UV light, it’s good to know a little bit more about UV itself. There are three classes of UV radiation – UVA , UVB and UVC. These groups are based on the measure of their wavelength, which is measured in nanometers (nm).
UVC (100-280nm) has the highest level of radiation. UVC from the sun is blocked by the ozone layer in the atmosphere, which means it doesn’t reach the earth’s surface. The only way you can be exposed to UVC radiation is from an artificial source, like a lamp or a laser. So, if you’re working with UVC sources, it’s important you wear appropriate specialist protection.
UVB (280-315nm) can’t penetrate beyond the superficial skin layers and is responsible for delayed tanning and burning. It increases skin ageing and is linked to the development of skin cancer. Most UVB from the sun is absorbed by the atmosphere.
Approximately 95% of the UV radiation that reaches the earth’s surface is UVA (315-400nm). It has lower energy than UVC or UVB but it can penetrate the deeper layers of the skin and is responsible for the immediate tanning effect. It contributes to skin ageing and wrinkling, and may increase the development of skin cancers.
I would recommend getting large-ish sunglasses to protect the skin around your eyes as well as your eyes themselves.
So, what about your eyes? UV exposure has been linked to the formation of pterygia. These are benign growths on the conjunctiva, which is the membrane that covers the white of your eye. So I would recommend getting large-ish sunglasses to protect the skin around your eyes as well as your eyes themselves. UV exposure has also been linked to the formation of cataract, and may increase the risk of age-related macular degeneration, although the jury is still out on that.
How to choose sunglasses that protect your eyes
It’s also important to make sure that the frame fits you well and is comfortable to wear, as sunglasses are less effective if they’re falling down your nose! If you get your sunglasses from an optical practice, they’ll adjust them for you so that they fit you comfortably. They’ll also do minor repairs for you, such as replacing a screw if it falls out.
Don’t be fooled into thinking that a dark lens will automatically absorb a safe amount of UV light – the depth of the tint has no impact on whether it absorbs the right wavelength.
As you can’t tell by looking at them which sunglasses absorb safe amounts of UV light, you should make sure you buy them from a reputable manufacturer (so not the local car boot sale…). You should also make sure they comply with the British Standard (BS EN ISO 12312-1:2013) or have the CE mark, which is the manufacturer’s assurance that they comply with the relevant safety standards.
You may see a label saying something like ‘UV 400’. This means that the lens will absorb a safe amount of radiation with a wavelength below 400nm. As light of wavelength 400nm is towards the blue end of the spectrum, these lenses may have an orange/yellow appearance if there is no other colour to disguise it. This may be cosmetically unattractive, so the manufacturer will probably add an additional colour to the lens, such as brown or grey. Don’t be fooled into thinking that a dark lens will automatically absorb a safe amount of UV light – the depth of the tint has no impact on whether it absorbs the right wavelength.
You can also protect your eyes and your face from the damaging effects of the sun by wearing a hat with a brim, or a sun visor.
Finally – don’t forget the children! Children often spend more time outdoors than adults do, and they have clearer lenses and larger pupils than adults. This means they are at greater risk of UV radiation reaching the inside of their eyes than adults, so it’s really important to remember to protect their eyes from the sun, just like you would protect their skin. You can find some really cute children’s sunglasses which aren’t expensive, and remember to get them a nice sunhat too!
My take-home messages for anyone looking to buy sunglasses are:
- If you’re going to be outside for a significant amount of time, protect your eyes and the skin around them with UV-absorbing sunglasses.
- As UV is invisible, you can’t tell by looking at lenses whether they absorb a safe amount of UV. So, buy your sunglasses from a reputable manufacturer and look out for any labels that tell you what protection they offer. They don’t need to be expensive to be safe.
- It’s particularly important to protect children’s eyes from the sun too, with sunglasses and/or a wide-brimmed sun hat.