UV Radiation: Its Impact on the Human Eye

By Marlene Jacobs and Werner Noeth

Did you know that UV can damage your eyes?

Light entering the eye penetrates through different levels the same way it penetrates your skin. Two different types of light enter the eye, namely UV light and Visible light. Fortunately we have the cornea and the crystalline lens to reduce the amount of UV rays entering our eyes, minimizing the amount of UV reaching the retina.

Some structures around the eye, like lids, lashes, eye brows etc, also provide some form of protection against UV. 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 can reduce penetration of the sun’s rays on a sunny day. On cloudy days, visible light is minimized but the exposure to harmful UV rays is still high.

Visible light increases the risk of macular degeneration and UV light increases the development of cataracts. Many people forget that the greater the exposure to UV radiation, the greater damage caused over a sustained period of time. But UV light isn’t all bad; 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.

3 TYPES OF UV RAYS EXIST:

UVA – Penetrates into deeper skin layers where connective tissue and blood vessels are affected. The crystalline lens absorbs UVA to help protect the retina. With pigment accumulation in the lens, age and a lifetime of UV exposure cataracts are very likely to develop. Fortunately cataracts can be removed and vision restored with an artificial lens. After surgery this form of surgery, UVA light can penetrate the eye with greater ease and therefore post-op UV protection is essential.

UVB – Causes sunburn and ‘snow blindness’ from reflection of water and snow, increasing likelihood of cancer. Light reflection off snow, water and sand increases the amount of UVB penetrating the eye. The cornea protects the eye against UVB but the conjunctiva stays exposed. UVB radiation can lead to the development of pterygiums and penqueculas; these are little white elevated tissue growths on the conjunctiva. They are not sight threatening, but can become uncomfortable, red and unsightly when exposed for to the elements. In severe cases they may lead to corneal problems and result in distorted vision. Surgical removal is possible.

UVC – is filtered by the ozone layer and has the highest energy UV rays, they are 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 the eye and typically are found in the iris (coloured part of the eye), cilliary body and choroid (structures in the eye).

HOW CAN YOU PROTECT YOUR EYES FROM THE SUN?

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 protecting 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 protect your eyes and 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 any UV light, 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™ and 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 the 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.

If wearing a tinted lens with no UV filter, UV 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 most definitely required. 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 save driving.

Your children are also in need of UV protection. They spend much 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.
• One should wear sunglasses even in the shade as surfaces do reflect UV rays which will
  still enter 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.
• Sunglasses aren’t just for people with light colored eyes, but for everyone
• 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.