‘Change your sunglasses every TWO years’

tunisante August 26, 2016 Health

Consistent exposure to sunlight wears down lenses in sunglasses
As a result, they break easier and give off less protection to UV rays
Insufficient lenses could damage the cornea and causes vision problems
Experts are now calling for new standards in testing the quality of shades

Stephen Matthews For Mailonline

Published:
19:00 EST, 25 August 2016

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Updated:
21:22 EST, 25 August 2016

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Sunglasses should be replaced at least every two years, scientists warned today.

Rays from the sun damage lenses over time – meaning they gradually let more UV light through and provide less protection.

Without adequate UV filters, the eye is exposed – and the damage can cause long-term, irreversible harm to vision.

Rays from the sun damage lenses over time – meaning they gradually let more UV light through and provide less protection

Brazilian researchers have now called for standards that test the quality of sunglasses to be revised, so that safe limits for the filters can be established.

They say a new test would guarantee sunglasses were safe to wear for a period of two years.

Exposure to sunlight varies across the world, but tropical countries have the highest amounts as UV levels are extremely high in summer and remain high in the winter.

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Therefore, sunglasses worn in the southern hemisphere may need replacing more often than in those worn in the northern half.

Lenses may also break more easily a result of consistent exposure to sunlight, experts say.

And wearing sunglasses which don’t offer proper protection can cause oedema – distorted vision from a swollen eye.

Experts say sunglasses worn in the southern hemisphere may need replacing more often than in those worn in the northern half

It can also result in cataracts – where the lens of the eye becomes cloudy, affecting vision – and pterygium – the growth of pink, fleshy tissue on the white of the eye which can interfere with sight.

WHAT ARE THE CATEGORIES OF SUNGLASSES?

Sunglasses are categorised based on how much light they let through to the eye – known as visible light transmission (VLT).

Darker glasses have a lower percentage while lighter shades have a much higher allowance.

Category 0: 80-100 per cent VLT

Suitable for:

Category 1: 46-79 per cent VLT

Suitable for: Fashion

Category 2: 18-45 per cent VLT

Suitable for: General purpose, watching and taking part in sport

Category 3: 8-17 per cent VLT

Suitable for: Open mountain ranges

Category 4: 3-8 per cent VLT

Suitable for: High altitude trekking and mountaineering.

Source: Ultralight Outdoor Gear

Prolonged UV exposure can also damage the macula – the part of the retina responsible for the majority of vision.

Professor Liliane Ventura, of Sao Paulo University, said: ‘Ocular health is a serious concern worldwide, but particularly in tropical countries where UV indexes are extremely high in summer.

‘In most countries in the southern hemisphere… sunglasses standards are not quite appropriate for the ultraviolet conditions.

‘Sunglasses play an important role in providing safety, and their lenses should provide adequate UV filters.’

The test currently used in Europe, Australia, New Zealand and parts of South America and calculates how badly the lenses deteriorate as a result of exposure to the sun.

It exposes sunglasses to a sun simulator for 50 hours from a distance of 30cm.

The 450 W lamp is the equivalent to two days in a natural environment on a summer’s day, or four in winter.

But Professor Ventura claimed the current test is ‘ineffective’ in its present form and doesn’t accurately measure the quality of sunglasses.

The findings were published in the journal Biomedical Engineering OnLine.