I received a telephone call from a patient the other day, who having watched the above episode of This Morning (apologies for the poor quality video!), was very keen to learn more about “these UV protected lenses that are clear”. With this still fresh in my mind, I wanted to attempt to set the record straight about UV / UV protection, and clear up any possible misconceptions.
In this blog I am purely referring to “incident” UV radiation, by which I mean naturally occurring UV (from the sun). Anybody that works with higher intensities of UV, such as someone manufacturing adhesives, WILL need extra protection, or risk damaging their eyes irrevocably.
I would also like to just reiterate that this is a personal blog – the opinions expressed here are purely my own and not those of my employer.
Your Eyes and UV – The Facts
The biggest problem that UV causes to the eyes is cataracts. This is a clouding of the lens in the eye that most people will experience as they get older – more than one in two people aged 65 and older have some signs of cataract, and it is present for almost everyone over 75. Some research has shown that smoking, poor diet & exposure to sunlight may accelerate cataract development1.
Now, before going any further, there is an important distinction to make clear, between UV protection and sun protection. UV protection on your glasses reduces the amount of harmful UV radiation that enters the eye. Sun protection shades us from the brightness of the sun, much like sitting in the shade or wearing a hat. Some people are very light sensitive, and to whom darkened or darkening lenses are a blessing. Confusion can arise because generally the two go hand in hand, in that most sunglasses offer some form of UV protection, however they are NOT mutually exclusive! There have been horror stories in the press only recently, about people whose eyes have been damaged by wearing sunglasses that didn’t offer sufficient (if any) UV protection – it’s important that you always check what you’re buying!
Ultraviolet (UV) radiation is part of the electromagnetic (light) spectrum that reaches the earth from the sun. It has wavelengths shorter than visible light, making it invisible to the naked eye. These wavelengths are classified as UVA (longwave), UVB (shortwave), or UVC, with UVA the longest of the three at 320-400 nanometers (nm, or billionths of a meter). UVB ranges from 290 to 320nm, whilst UVC has even shorter rays, most of which are absorbed by the ozone layer and do not reach the earth2. Beyond each end of the visible spectrum lie wavebands of radiation which, although they cannot be detected by the visual mechanism, are included in the optical range of radiation3, but are not considered to be hazardous to the eyes.
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Both UVA and UVB do penetrate the atmosphere and have been demonstrated to play an important role in conditions such as premature skin aging, eye damage (including cataracts), and skin cancers. It was once thought that only UVB was of concern, but more and more is being publicised about the damage caused by UVA. Most of us are exposed to large amounts of UVA throughout our lifetime. UVA rays account for up to 95 percent of the UV radiation reaching the Earth's surface. Although they are less intense than UVB, UVA rays are 30 to 50 times more prevalent. They are present with relatively equal intensity during all daylight hours throughout the year, and can penetrate both clouds and glass2.
The term “UV400” denotes lenses that absorb UV up to 400nm, and ideally if you are buying “off the shelf” sunglasses from the high street or online – this is what you want to be sure you’re getting!
With regard to prescription spectacles, a standard 1.5 index hard resin (CR39) lens will protect against the more intense UVB radiation (100% cut @ 340nm), but a separate coating can be applied to these to make them 100% UV protected, i.e. against UVA AND UVB (100% cut @ 395-400nm)5. All other higher index materials (“thin & light”) will naturally absorb 100% incident UVA and UVB and therefore no additional protective ‘coating’ is required. The same is true for hard resin photochromic (light-reactive) lenses.
So, if you have Polycarbonate, Trivex, 1.6, 1.67, 1.74 or hard resin photochromic lenses, and you’ve paid an addition for UV protection – you may have been mis-sold!
Children and UV Protection
There is a somewhat “old school” way of thinking, that children shouldn’t wear sunglasses, as it may over-sensitise them to sunlight. However, there is arguably more incident UV in the present day, than there was 50+ years ago, as a result of the hole in the ozone layer. Nobody would argue that protecting your child’s eyes from UV radiation is a bad thing. Again, it comes down to the fact that there is a difference between protecting their eyes from UV, and shielding them from the brightness of the sun.
Personally, as a Dispensing Optician I feel that there is no problem with putting children in sunglasses if it is limited to the times they are actually outside in the sun, especially if on a sunny family holiday abroad for instance. My worry is that in this modern celebrity-obsessed era, where celebrities are pictured wearing sunglasses inside and outside, and at all hours of the day and night, impressionable children may want to do the same, and sometimes even with the strongest willed of parents, resistance is futile.
THIS is where problems could arise, especially if the child in question requires a corrective prescription lens in their glasses. You see, when we wear sunglasses, our pupils dilate to allow the maximum amount of light into the eye, so as to produce the sharpest possible image. If a child’s pupils are constantly dilated, this could in theory reduce their visual acuity and hence increase their prescription and/or their need for it. This is something we do not want happening!
Used correctly, I have no issue with children wearing sunglasses, and there are some awesome ones out there…
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…it is just important to establish some “ground rules” for wearing them? Sunglasses are not merely a fashion accessory.
So, there’s my two-part UV rant over. I hope you’ve found this blog post both informative and useful? As always, if you have any questions, or feel there’s an area I’ve neglected to cover, please do not hesitate to contact me – it would be wonderful to get your feedback!
References
- Agius, N. (2015) This Morning viewers urged to wear sunglasses all year round.Retrieved August 7th, 2015, from www.mirror.co.uk
- http://www.abdo.org.uk/information-for-the-public/eyecare-faq/cataract/
- http://www.skincancer.org/prevention/uva-and-uvb
- Jalie, M. (1972). The Principles of Ophthalmic Lenses. London: The Association of Dispensing Opticians.
- http://light-measurement.com/wavelength-range/
- Figures from the 2014/15 Hoya Lens Catalogue.
- Photo courtesy of www.esprit.co.uk.
