About UV Light
Ultra-violet light (UV) is invisible to the human eye. It is that part of the light spectrum which causes damage to the eye over time. UV is divided into 3 segments namely A, B and C. UVC is filtered by the earth’s ozone layer; UVB causes sunburn and snow blindness, and is absorbed by the cornea; UVA passes through the cornea and is absorbed by the crystaline lens and the retina. Therefore UVA and UVB radiations are the greatest concern as they are the most damaging to the eye.
UVA: 320-400nm (longest wavelength)
UVC: below 286nm (shortest wavelength)
Other sources of UV radiation include: welder’s flash, flourescent lighting, high intensity mercury vapor lamps (for night sports and high-crime areas).
Long-Term Effects of UV Radiation
As the cornea absorbs UVB radiation, it is vulnerable to the development pterygia (benign growths of tissue on the white part of the eye), pingueculae (localized tissue growth on the white), snow blindness and photokeratitis (sunburn to the first tissue layer of the cornea) leading to reduced vision.
Bombardment of UVA radiation on the lens causes a photochemical change. This results in cataracts (clouding of the lens) being formed over time and eventually causes blindness until such a time that the lens is replaced.
UVA also causes damage to the retina resulting in Age-related Macula Degeneration (ARMD) in persons over 55 years of age and solar retinitis (macula hole). Both conditions lead to irreversable reduced vision.
What Can I Do?
Try to minimise the effects of bright light and glare, and reduce luminance to more comfortable levels. You can protect your eyes by wearing a wide-brimmed hat and a good pair of sunglasses.
Prescribed spectacles can also provide you with full UV protection without compromising the clarity of your lenses.
Good sunglasses eliminate the need to squint, reduce strain and decrease the impact of harsh glare.
Here are some tips on what to look for when purchasing your sunglasses:
- Always ensure that the lenses have 100% UV protection. This should be indicated on the product label.
- The choice of a lens colour (tint) and its darkness would depend on the function you intend to use your sunglasses for. Different activities require different tint intensities. Lenses darker than 85% will start reducing your vision. Neutral grey absorbs light in the same proportions, and thus does not change the colour spectrum but provides true colour definition. Polarised lenses reduce reflected glare, reducing eye fatigue and promoting vision, and are especially suitable for high glare environments such as marine sports. Amber lenses provide high contrast and are very effective with eg clay-pigeon shooting.
- Lenses made of glass break more easily than plastic, are heavier than plastic but are less likely to scratch. But remember that plastic and polycarbonate lenses are safer (sports).
- Non-prescription lenses should be tested for visual distortion. This can be done by holding the sunglasses at an arms length, close one eye and look through the lens at a rectangular pattern (e.g. floor tile). Move the sunglasses from side to side and up & down. If the lines become wavy or wiggle, there is distortion in the lens and you should not buy the sunglasses.
- The sunglasses should feel comfortable and fit your face.
- Depending on the purpose of the sunglasses, check that the frame does not interfere with your peripheral vision.
Proper UV protection is essential noon-to-dusk. You wouldn’t go to the beach without sunscreen. Don’t your eyes deserve the same protection?