Lonely Planet Writer

Sunglasses should be changed every two years to protect eyes from sun damage say scientists

New scientific research suggests that sunglasses should be replaced every two years to protect eyesight against ultraviolet rays. Exposure to the sun is now believed to wear down the protective lensing even in designer sunglasses, leading to increased risk of damage through exposure.

Designer sunglasses now
Designer sunglasses now have a shelf life of two years.   Image by Getty Images

Scientists at the University of Sao Paolo in Brazil say that if sunglasses aren’t replaced, the wearer runs the risk of long-term degeneration of vision. Global News reports that the study recommends that individuals should replace sunglasses every two years to avoid the prospect of impairment. Gismodo.com.au report that in Australia there are both regional and national standards on the level of protection sunglasses provide against UV rays.

The website says that there is now a need to revise the standards by establishing safe limits for the UV filters in the lenses. Testing the ageing of lenses in Europe, Australia, Brazil and New Zealand is undertaken to measure the scale of deterioration due to exposure to the sun.

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Due to a higher IC index sunglasses in the southern hemisphere should be replaced more frequently than those in the northern hemisphere Image by Sarah Joy / CC BY-SA 2.0

The aim is to ensure lenses have sufficient UV filters as inadequate levels could affect the cornea and internal structure of the eye. When this happens, edema or swelling to the eye can cause distorted vision. Pterygium or the growth of fleshy pink tissue on the white of the eye can also affect vision while other side effects can result in retina damage or cataracts. Researcher Liliane Ventura explained that 50 hours of exposure to the sun simulator was the equivalent to exposure of 23.5 hours natural sun in Brazil. While exposure varied depending on geographical location, tropical countries caused most concern because UV indexes were very high there in summer and remained so in winter. So if you live in a hot spot in the southern hemisphere you need to replace your sunglasses more than those in the northern hemisphere.

Beach reflection in sunglasses
There is now a need to revise the standards by establishing safe limits for UV filters in lenses. Image by: Getty Images

Researcher Liliane Ventura explained that 50 hours of exposure to the sun simulator was the equivalent to exposure of 23.5 hours natural sun in Brazil. While exposure varied depending on geographical location, tropical countries caused most concern because UV indexes were very high there in summer and remained so in winter.