Virtual Medical Centre

Sun Protection for Your Eyes

• Introduction to eye protection
• What eye diseases are associated with exposure to sunlight?
• Environmental factors and UV exposure

Introduction to eye protection

Eyesare sensitive instruments which can easily become injured or diseased from exposure to sunlight, because of the ultraviolet (UV) rays of the sun. Ultraviolet rays are high energy,and areinvisible to the human eye because they are outside the spectrum of colours that a human eye can see.

The eye, by its design, naturally provides some protection against UV rays. For example, eyelidswill partially close to cover the eyein a squint when exposed to strong light. However, the eye's natural protection is only partial, and any exposure to sunlight creates a risk of developing eye diseases and disorders. The extent of the risk variesdepending on both the quality (e.g. the angle of the sun's rays) and quantity (i.e. length of exposure) of sunlight, and the protective measures taken by an individual to reduce eye exposure to UV rays while in sunlight.

What eye diseases are associated with exposure to sunlight?

Exposure to sunlight can cause damage to the eyes in both the short and long tem. In the short term, exposure to sunlight can result in:

• Mild irritation: May cause symptoms such as excessive blinking, swelling or difficulty seeing in strong sunlight.
• Photo Keratoconjunctivitis: Photo keratoconjunctivitis is a condition similar to snow blindness or welder's flash burn. It occurs when the sensitive, skin-like tissues of the eyeball become sunburnt. Individuals suffering from the condition are likely to experience severe pain, and possibly temporary blindness, for 12 days. The condition is temporary and will resolve naturally.

In the long term, exposure to sunlight is associated with a range of eye diseases, including:

• Eye cancer (also known as squamous cell carcinoma of the eye): A rare condition characterised by the growth of cancerous cells on the surface of the eye. The World Health Organisation (WHO) estimates that5070% of eye cancers around the world are caused by sun exposure. The risk of developing eye cancer increases with lifetime exposure to sunlight. The incidence is highest in countries closest to the equator.
• Cortical and posterior subcapsular cataract: Cataracts are characterised by the increasing opaqueness of the lens of the eye. It can lead to impaired eye sight and, in severe cases, to blindness. The WHO estimate 5% of cortical cataract disease is caused by sun exposure. In Australia, the Australian Cancer Council estimates that up to 10% of all cataracts are associated with excessive sun exposure. A study of a United States population found that individuals who had high levels of sun exposure were about 1.5 times more likely to develop cortical or posterior subcapsular cataracts than those who had low sun exposure, while those with moderate sun exposure were about 1.2 times more likely to develop each of these types of cataracts.
• Pterygium: Pterygium is characterised by a fleshy growth on the eye's surface. The WHO estimates that 4070% of the global burden from this disease is attributable to sun exposure. A study conducted in Victoria reported that 43.6% of pterygium cases were attributable to sun exposure.
• Age related macular degeneration: Based on laboratory studies showing thatUV rays cause retinal damage in rats, scientists believe that exposure to UV rays contributes to the degeneration of eyesight which occurs naturally with ageing.

Environmental factors and UV exposure

The level of UV radiation varies due to a range of environmental factors,including:

• Time of day: UV radiation levels are highest when the sun is higher in the sky (in the middle of the day, between 10am and 2pm).
• Geographic location: UV radiation levels increase with increasing proximity to the equator, and increasing altitude.
• Cloud cover: UV radiation levels are higher when there is no cloud cover, although UV radiation from the sun is present even on cloudy days.
• Features of the surrounding landscape: As UV radiation from the sun is reflected more or less effectively by some surfaces than others, exposure to UV radiation is also influenced by features of the surrounding landscape. Snow is a particularly reflective surface, and as much as 80% of UV radiation will be reflected back (compared to about 10% for water and grass). Dry beach sand reflects about 15% of UV radiation, while the foam in sea water reflects 25% of UV radiation.
• Ozone protection: A layer of ozone forms a protective layer around the earth and blocks much of the suns harmful rays, including much UV radiation. Ozone levels vary between places and times of the day.