When you buy a counterfeit designer bag, piece of clothing, watch, or pair of shoes, the worst outcome is usually minor - perhaps a sole comes loose, or a watch hand falls off. These faults are frustrating, but they don’t pose a health hazard in the way counterfeit sunglasses can.

Mr Alex Day, a leading Consultant Ophthalmologist at Moorfields Private Eye Hospital, cautions that buying fake sunglasses is effectively gambling with your sight - an act that could lead to irreversible, long-term damage to your vision.

"Counterfeit eyewear is uniquely dangerous because it usually features dark-tinted lenses with absolutely zero UV protection,” he says. “From a medical perspective, wearing them is actually significantly worse than wearing no sunglasses at all."

Mr Alex Day

The connection between fake sunglasses and ‘dilation danger’

It’s not always true that higher-priced sunglasses guarantee superior UV protection. However, established brands are more likely to meet safety regulations and clearly display appropriate certification.

According to Day, buying imitation designer sunglasses can expose you to a physiological risk known as ‘dilation danger’.

"When you step into bright sunlight, your pupils naturally constrict to reduce the amount of light entering the eye,” he explains. “When you put on dark sunglasses, your brain is tricked into thinking you are in a dark room, causing your pupils to dilate and open up.

"If those sunglasses are counterfeit and lack UV filters, you are effectively opening the floodgates, allowing a massive, unfiltered dose of harmful UVA and UVB radiation to penetrate straight through to the lens and retina."

Day adds that, over time, this intense UV exposure causes cumulative cellular damage.

Long-term exposure to unfiltered sunlight can increase your chance of developing:

• Cataracts - where the usually clear lens of your eye becomes cloudy.

• Pterygium - growths of tissue over the clear cornea of your eye.

• Eyelid cancers.

• Retinal issues - such as age-related macular degeneration.

The most reliable way to choose a safe pair of sunglasses this summer - whether designer or not - is to carry out a simple 'safety check' before you buy.

"Ultimately, your sunglasses should be seen as safety equipment first and a fashion accessory second," concludes Day. "A £15 pair of pharmacy sunglasses with the correct safety marks will protect your eyes infinitely better than a £30 fake 'designer' pair."