Glaring omission can cost vision

PUBLISHED : Tuesday, 30 August, 2011, 12:00am
UPDATED : Tuesday, 30 August, 2011, 12:00am


Most people associate overexposure to the sun with skin cancer but are less aware of its effect on the eyes and just how important it is to wear a pair of good sunglasses.

The sun emits light of different wavelengths, including ultraviolet radiation in the UVA, UVB and UVC bands.

UVA rays are closest to visible light rays and have the lowest energy among the three bands. They pass through the cornea and reach the lens and retina.

Overexposure to UVA rays has been linked to the development of certain types of cataracts.

UVB rays, with a slightly shorter wavelength than UVA rays, are partially filtered by the ozone layer but still reach the earth's surface.

Moderate doses of UVB radiation stimulate the production of melanin - which results in the golden tan that beach-goers long for. In higher doses, however, they cause sunburn, increasing the risk of developing skin cancer as well as premature signs of skin ageing, such as wrinkles.

UVC rays have the highest energy and are the most harmful to the eyes and skin. Although the ozone layer blocks almost all UVC rays from reaching the earth, its gradual depletion could mean increased exposure and more health-related complications in future.

When UV rays enter the eye, they are absorbed by chromophores, substances in the eye cells and tissues that absorb light energy, triggering a series of molecular changes that enable light signals to be transmitted to the brain, producing sight.

Unlike the skin, which adapts to UV radiation by producing melanin, the eye has no protection from exposure to strong sunlight. If too much UV light is absorbed, the cornea, lens and retina can be damaged.

The bad news is that the average Hongkonger is likely to develop eye damage related to sun exposure in his or her lifetime. Every person will develop cataracts - if he or she lives long enough - says Dr Chng Nai Wee, an ophthalmologist at the Singapore-based Eagle Eye Centre.

According to the World Health Organisation, cataract is the world's leading cause of blindness. It is responsible for 30 per cent of blindness and low vision in Hong Kong patients. In 2008 alone, nearly 20,000 people in Hong Kong were diagnosed with cataract, which forms when the lens of the eye becomes clouded because of wear and tear on its protein fibres.

Cataracts can form at the back, on the periphery or deep in the central zone of the lens. They develop gradually and may go undetected for months or years.

Eventually, eyesight begins to be affected; blurred vision, haloes around lights and glare from the headlights of oncoming cars at night are common. If left untreated, the lens will liquefy and become totally opaque, leading to blindness.

With advances in surgery, cataracts can be taken care of quickly in a day surgery under local anaesthesia. The clouded lens is removed and replaced with an intra-ocular lens implant that will offer regular vision or correct presbyopia (long-sightedness), depending on the patient's lifestyle needs and budget.

Another complication that can develop when the eye is exposed to too much sun is solar maculopathy. The lens of the eye acts very much like a magnifying glass. When too much light enters the eye, it burns the centre of the retina at the back of the eyeball, an area called the macula. Only 20 seconds of sun gazing will result in a burn.

'Solar maculopathy is due to damage to the photoreceptor cells at the macular area. UV light causes photochemical injury to the cells in the retina, causing permanent damage to the macula,' Dr Alan Ng, an ophthalmologist with a private practice in Mong Kok, says.

The extent of the damage depends on the duration of exposure, the position of the sun in the sky at the time and the individual's eye health. Symptoms include blurred vision, headache, blind spots in vision and distorted vision. Solar maculopathy is not treatable.

The sun can also cause problems with the conjunctiva - the transparent mucous membrane that lines the white (sclera) of the eye and the insides of the eyelids. Pterygia (pronounced tuh-rij-ee-ya) and pinguecula (ping-gwek-you-la), which are common, non-cancerous growths on the cornea and conjunctiva, may develop as a result of prolonged sun exposure.

A pinguecula is caused by the degeneration of the conjunctiva's collagen fibres. The original transparent fibres are gradually replaced by thicker yellow fibres, or calcified deposits. A pterygium, which often develops from pinguecula, is a triangular-shaped growth that may eventually extend over the cornea, causing vision problems.

Both conditions usually do not require treatment unless symptoms are severe or vision is affected. Lubricating or mild steroid eye drops are usually prescribed to relieve the symptoms. In serious cases, an ophthalmologist may surgically remove the growth.

'Pinguecula and pterygia may require surgery when the growth is very thick, causing irritation while blinking,' Ng says. 'A pterygium can grow into the cornea, causing astigmatism. It may also grow towards the centre of the eye, obstructing the visual axis. In these circumstances, surgery is indicated.' Younger patients may also opt for surgery because of cosmetic concerns.

Protecting your eyes from sun damage is as simple as buying a pair of good sunglasses. Look for a pair that guarantees at least 99 per cent protection from UVA and UVB rays.

They should fit as close to the face as possible. Wrap-around styles are best, as they provide better coverage of the eye area. For extra protection, wear a large-brimmed hat.

If you plan to engage in water sports or fishing, you may want to consider sunglasses with polarised lenses. These lenses reduce glare from reflective surfaces, such as the surface of the sea, by allowing only vertically polarised light to enter the eyes. Chng says that their advantage will mainly be appreciated by sportsmen. 'For the layman, a pair of 100 per cent UV-blocking wrap glasses will do fine,' he says.

The time of day you choose to get your dose of sunshine also matters.

'Avoid exposure to the midday sun,' Ng advises.

The sun is at its highest overhead and is therefore strongest between 11am and 3pm. While this is the time that many sunbathers will choose to work on their tan, it is also when the highest levels of UV damage occur.

Even if the day seems cloudy or overcast, UV rays can still penetrate cloud cover and reflect off water and concrete. If you must be outdoors, sunglasses and a hat will keep you looking and feeling cool.

Safety with style

Keeping your peepers safe from the sun's dangerous rays need not be an unfashionable affair. Moh Lee, an optician and fashion eyewear consultant at Eyes@Work in Singapore, recommends five shades that will have you soaking up the sun in style. From the top:

Alain Mikli AL1070

Theo 'Beech'

Jeremy Tarian 'Sky Bar' (polarised)

Barton Perreira 'Noble'

Starck Biosun PL0804 (polarised)