UV Radiation
 – Its Effect on the Eye

The human eye, by definition, is only sensitive to visible light, at least for vision. UV radiation does, however penetrate the eye to a certain extent, and can therefore do damage if exposure is sufficiently intense or prolonged. UVB is fully absorbed by the cornea while UVA reaches the lens. Less than 1% of all UV radiation on the eye reaches the retina.

The effects of over-exposure to UV can be as simple as excessive blinking, difficulty looking at strong light, and swelling, and these effects typically disappear fairly quickly after the exposure ceases and generally do not result in long term damage.

More serious over-exposure can cause photokeratitis and photoconjunctivitis, inflammation of the cornea and conjunctiva, respectively. These conditions are effectively sunburn of these delicate tissues and appear within a few hours of exposure. Although the effects can be painful they are reversible and generally do not cause long term harm.

Extreme cases of photokeratitis are often known as snowblindness, since they most often affect climbers and skiers who are subjected to high levels of UV from the combination of high altitude and reflections from snow. Prolonged exposure to such extreme UV levels kills the outer cells of the cornea, which become opaque and cause blindness. The condition can be very painful as the dead cells are shed, but new cells grow quickly to replace them and vision is normally restored within a few days.

Excessive UV exposure can also have much more long term and serious effects:

  • Cataracts – clouding of the lens that causes images to look blurred and eventually leads to blindness. It is estimated that up to 20% of cataracts worldwide are caused by UV exposure. Once sufficiently developed, cataracts can be surgically removed and the lens replaced with an artificial version.
  • Pterygium – a wedge-shaped opaque growth of the conjunctiva. This is a common cosmetic blemish but in extreme cases the growth can extend over the cornea and cause loss of vision. The growth can be surgically removed, but tends to regrow.
  • Macular Degeneration – permanent loss of vision due to destruction of the cells of the retina, particularly in the centre. Although this is primarily an age-related condition, over-exposure to sunlight is believed by some to be a contributory factor.
  • Cancers – various parts of the eye can also be subject to cancers, including the conjunctiva and iris. The eyelids can be affected by skin cancers and melanoma can also affect the iris. There are also many other areas of the eyes that can be affected by cancer, but UV exposure does not appear to be a significant risk factor in their development.

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