By Cheah Ui-Hoon

EVERYONE knows that if you are out in the sun for too long you'll get sunburn. But few know that if you're in the sun without sunshades for too long, your corneas will also suffer from sunburn.

The effects and damage of UV radiation on the eyes can be extensive, says Dr Julian Theng, medical director of the Eagle Eye Centre. 'Our eyes are made up of various layers of tissue that absorb different wavelengths of the ultra-violet rays, and each of these layers can respond quite differently,' he says.

Prolonged exposure to UV rays can cause corneal cell damage - sunburn on the cornea. What happens is that UV rays absorbed by the crystalline lens in our eyes lead to lens opacification, also known as cataract formation.

'UV rays that are absorbed by the retina have been implicated in macular degeneration and damaging retinal tissues,' Dr Theng adds.

Two of the most common and well documented ailments associated with exposure to UV rays are pinguecula and pterygium. A pterygium is a reddish, fleshy piece of tissue that grows in a triangular shape over the cornea.

'It usually occurs on the inner corner of the eye and grows towards the pupil, though it may also appear on the outer corner. A pterygium tends to grow slowly and although relatively harmless, it could grow large enough to covers the pupil or eye and, as a result, interfere with vision,' says Dr Theng.

A pinguecula, on the other hand, is seen as a yellowish/white growth (bump) of the mucus membrane lining the eyeball and underside of the eyelids (conjunctiva). Unlike a pterygium, a pinguecula does not actually grow on to the cornea, but the 'bump' can cause considerable irritation.

Although the exact causes of these complaints aren't known, long-term exposure to sunlight - especially UV rays - appears to be the most likely contributing factor.

'Hence, pterygium tends to occur more frequently in those who spend a lot of time outdoors and is more commonly found in hot tropical climates and usually within the people in the 20-40 age group,' says Dr Theng.

Men are also more susceptible to these two conditions, as they tend to spend more time than women outdoors.

Dr Theng says reassuringly that in most cases, pterygium and pinguecula are considered benign eye conditions.

Symptoms include persistent redness, inflammation, foreign body sensation or dry and itchy eyes.

'But in advanced cases of pteryigum, the pytergium could invade the cornea, affecting vision with the potential of induced astigmatism and corneal scarring.'

Eye drops or ointments may be used to soothe the inflammation. However, for pterygium cases, this will not halt the growth.

'When the pterygium grows too large and begins to threaten sight, we would recommend having it surgically removed,' says Dr Theng.

'As part of the procedure, a patch of translucent skin called the conjunctiva is used to patch over the site of removal,' he explains.

'The chances of a pterygium growing back after removal are low. Though uncommon, it may return, but this usually affects the younger generation who are constantly exposed to sun's UV rays.'

Not surprisingly, Singapore being almost on the equator means we're exposed to huge doses of direct sunshine, with the sun almost directly overhead throughout the year, says Paul Peiffer, managing director Asia for Transitions Optical.

He advises care in the selection of the lens, if you're making glasses. 'Transitions lenses continuously block 100 per cent of UVA and UVB rays, so you can protect your eyes from harmful UV rays,' he says.

Even if you have good eyesight, you should have eyewear that blocks 100 per cent of UV light, says Mr Peiffer. 'Sunglasses don't necessarily offer the right protection - just because they are dark does not mean they have proper UV blocking technology. Therefore it's important to get eyewear with UV400 protection.'

Dr Theng agrees, as another thing UV rays do is cause damage to the pigment cells in the retina.

Overall healthy habits help also, says Dr Theng. 'A proper diet, regular exercise and rest. Smoking impairs blood circulation and decreases the efficiency of the retinal vessels.'

You can check the forecast of UV levels for any city worldwide at: http://asia.transitions.com/healthysight/uv/local.htm

This article was first published in The Business Times.