Jason Yosar, The University of Queensland

The iconic “Slip Slop Slap” campaign was launched in Australia in 1981. Sid the Seagull encouraged people to slip on a shirt, slop on sunscreen and slap on a hat to minimise ultraviolet (UV) radiation exposure and reduce the risk of sunburn and skin cancer.

In 2007, the slogan was updated to “Slip Slop Slap Seek Slide”. So now it includes seeking shade and sliding on sunglasses to further reduce the risk of UV-related damage. This emphasises the importance of protecting eyes – and the skin around them – from UV radiation.

Short-term effects

Briefly exposing an unprotected eye to UV rays usually won’t cause any symptoms.

But prolonged or intense UV exposure without eye protection (including to the sun, welder’s arcs, snow and tanning beds) can cause a condition called photokeratitis.

This can be thought of as sunburn of the cornea, the clear window on the front of the eye. UV rays cause death of the outermost layer of cells of the cornea.

This results in severe pain affecting both eyes, which begins six to 12 hours after exposure.

Treatment involves oral painkillers and antibiotic eye ointments (to prevent infection of the damaged cornea) while waiting for the corneal cells to regenerate.

The process takes 24 to 72 hours and people can expect a full recovery with no complications from photokeratitis.

Long-term effects

Repeated exposure to UV radiation without adequate eye protection can result in permanent eye damage. Eye diseases associated with chronic UV exposure include the following.

Cataracts

Here, the normally transparent lens of the eye becomes cloudy. This causes blurred vision and eventually blindness if untreated. It is estimated up to 20% of cataract cases are caused or made worse by UV exposure.

Wearing sunglasses remains one of the most effective ways of preventing cataract formation.

When they cause troublesome visual impairment, cataracts require surgical extraction. This costs Australia more than A$320 million a year.

Pterygium

This is a benign growth of conjunctival tissue on the cornea. The conjunctiva is the transparent membrane overlying the sclera (the white part of the eye) and usually does not cover the cornea. Although non-cancerous, the presence of a pterygium can cause chronic irritation, redness and inflammation.

Pterygia grow slowly over months and years and can obstruct vision when they grow over the pupil. They may also induce astigmatism (an improper curvature of the cornea), which blurs vision.

Treatment for mild pterygia not affecting vision involves lubrication with artificial tears. Those that affect vision may require surgical excision.

Again, chronic UV exposure to unprotected eyes is a major cause of pterygium development.

Macular degeneration

This is a degenerative disease affecting the central part of the retina (the macula) responsible for central vision. Macular degeneration may result in severe visual impairment.

Treatment comprises injections of medications directly into the eye and aims to limit disease progression; it cannot reverse damage that has already occurred.

While the link between UV exposure and macular degeneration is less clear than with cataracts or pterygia, short-wavelength radiation and blue light (present in bright sunshine) cause damage to the retina. There is a correlation between light exposure and macular degeneration.

Wearing sunglasses is therefore important to limit excessive light exposure of the retina.

Cancer

Although less common, chronic UV exposure is associated with increased rates of certain types of eye cancers. These are: squamous cell carcinoma of the conjunctiva, melanoma within the eye, and skin cancers of the eyelid and around the eye where people do not routinely apply sunscreen.

Treatment of these cancers may sometimes require surgical removal of the entire eye.

Climatic droplet keratopathy

This is a rare disease caused by UV exposure in which the cornea becomes cloudy, obstructing vision and potentially requiring a corneal transplant to restore vision.

What kind of sunglasses should I wear?

All sunglasses sold in Australia are regulated under the Australian/New Zealand Standard for sunglasses and fashion spectacles, which assigns a category from zero to four for each pair of sunglasses.

Categories zero and one aren’t sunglasses and so aren’t considered adequate for UV protection. Categories two to four provide effective UV protection and increasing levels of sun glare reduction (although category four must not be worn when driving).

It’s important to note price is not an indicator of effectiveness in UV protection. Effective sunglasses should be close-fitting and wrap-around to minimise the amount of UV radiation that can reach the eye.

Some contact lenses also contain UV filters. However, as they cover only the cornea, they provide no protection against the development of pterygia or cancers on or around the eye.

When should I wear them?

Sunglasses should be worn at all times when outdoors during the day when the UV index is 3 or above as there is no defined “safe level” of eye exposure to UV radiation.

They should also be worn regardless of cloudiness, as more than 90% of UV rays can penetrate through cloud. UV rays also reflect off sand, water and snow. The daily peak period of UV exposure is between 10am and 2pm; seeking shade during these hours is preferable.

The eyes of children are particularly susceptible to UV radiation, so children should be encouraged to wear sunglasses as soon as they can tolerate them.

Jason Yosar, Associate Lecturer, School of Medicine, The University of Queensland

This article was originally published on The Conversation. Read the original article.