Johannesburg, 5 November 2013 – Two different types of light enter the eye, namely Ultra Violet (UV) light and Visible Light. UV light cannot be seen by the naked eye whereas visible light such as sunlight entering a room can be seen. Fortunately we have the cornea (front of the eye) and the lens in the eye which absorb UV light and reduce the amount of UV rays reaching the retina (the back of the eye).
Davor Jadrijevic from VISION Optometrists in Cresta, Johannesburg explains that when visible light penetrates the eye, it falls on the retina and stimulates photoreceptors in order to produce an image. “Visible light (not UV radiation) causes pupil constriction, eyelid closure and squinting which can reduce penetration of the sun’s rays on a sunny day.” Jadrijevic continues by warning that, visible light is minimised on cloudy days but the exposure to harmful UV rays is still high. Physiological structures around the eye, like lids, lashes and eye brows also provide some form of protection against UV.
UV light and shorter wavelengths of blue visible light increase the risk of macular degeneration* and the development of cataracts**. According to Jadrijevic, many people forget that the greater the exposure to UV radiation on a regular basis, the greater damage caused over a sustained period of time. Luckily it’s not all doom and gloom and UV is useful to the human body, as Jadrijevic explains; “We certainly need it for Vitamin D production. Vitamin D helps in strengthening bones, protects us against diseases, helps to increase calcium and phosphorus absorption from food, and enhances blood circulation.”
Three types of UV rays exist:
UVA penetrates into deeper skin layers where connective tissue and blood vessels are affected. The crystalline lens in the eye absorbs UVA to help protect the retina. Continuous absorption of UV light by the lens of the eye results in connective tissue breakdown and degenerative changes within the lens. With age and a lifetime of UV exposure cataracts are very likely to develop. With the latest technology cataracts can be removed and vision restored with an artificial lens. After surgery care is essential as UVA light can now penetrate the eye with greater ease and Jadrijevic advises that patients invest in a decent pair of sunglasses to be worn whenever outdoors.
UVB causes sunburn and ‘snow blindness’ from reflection of water and snow, increasing likelihood of cell damage. Light reflection off snow, water and sand increases the amount of UVB affecting the eye. The cornea protects the eye against UVB but the conjunctiva (the mucous membrane that covers the front of the eye and lines the inside of the eyelids) stays exposed. UVB radiation can lead to the development of pterygiums and pingueclas; these are little white elevated tissue growths on the conjunctiva. They are not sight threatening, but can become uncomfortable, red and unsightly when exposed to the elements. In severe cases they may lead to corneal problems and result in distorted vision. Surgical removal is possible.
UVC is absorbed by the ozone layer and has the highest energy UV rays which make them the most harmful to your eyes.
Scientists have shown that many forms of eye cancers might be caused by lifelong exposure to the sun and its harmful radiation. Uveal Melanoma is the most frequent malignant cancer of the eyeball and more often than not, requires surgical removal. Other cancers can be found in and around the eye and typically are found in the eyelid, iris (coloured part of the eye), cilliary body and choroid (structures in the eye).
Protecting your eyes
Spectacles with UV coatings, sunglasses, large brimmed hats and visors are some measures you can employ to protect you from the dangers of UV. Clear prescription spectacles (without a UV coat) do provide some form of protection but not the full 100% and you remain at risk.
When choosing spectacles to protect your eyes from UV, certain aspects need to be considered:
- Frame: A wraparound frame and/or curved shaped lenses are better than flat shaped lenses. They not only protect most of the eye, they also shield the skin around the eyes from all light rays and reflections.
- Lens material: The standard plastic lens gives 92% protection whilst a glass lens doesn’t absorb much UV light at all, therefore providing no UV protection. Modern materials like polycarbonate lenses provide total protection from UV.
- Coatings: UV filter is essential and gives 100% protection against UVA, B and C, can be used on sunglasses and clear lenses
- Transitions™: (variable tint/photochromatic) lenses provide 100% protection against UV radiation. These coatings are activated by UV light and not visible light, therefore the amount of darkening depends on temperature and sun light.
- Tint: Brown and tan lenses provide the best protection against UV and visible light, it blocks 95% of blue light and doesn’t distort colours.
When wearing a tinted lens with no UV filter, UV rays will flood into the eye and expose the retina. This is as a direct result of the tinted lens blocking visible light and thereby prevents the pupil from constricting. This simply allows more UV to pass into the eye.
When one spends a lot of time on the beach or on water, maximum ‘blue light’*** protection, 100% UV protection and glare reduction are a requirement. Short wavelength blue light can cause macular degeneration. It is shown that brown and tan tinted, UV coated lenses will provide the best protection.
When you spend a lot of time in your car, 100% UV protection is required, but at the same time, sufficient visible light should be allowed through the lens for safe driving.
Your children are also in need of UV protection. They spend more time outside and are at risk of potential damage to their eyes and skin. Provide your kids with good quality sunglasses and encourage them to wear brimmed hats on sunny days.
Interesting facts about UV
- Not all sunglasses give 100% protection against all the UV rays so ensure you buy sunglasses from a reputable source.
- One should wear sunglasses even in the shade as surfaces like table tops and beach sand still reflect UV Rays into your eyes.
- It is advised that you continue to wear sunglasses when overcast, as UV exposure is often very high in those conditions.
- Even when wearing contact lenses that block UV, you will still require sunglasses as the contact lens only protects the area it covers and not the conjunctiva or skin around the eyes.
- Large brim hats and visors can reduce up to 50% of UV and visible light.
- Transitions or photochromatic lenses are not advised when skiing downhill as dangerous ice patches might appear invisible.
- Cataracts are the leading cause of blindness in the world.