People could risk eye damage using sunglasses that have 'gone off'

People are only just realising that sunglasses can actually 'expire', potentially leaving eyes vulnerable to lasting harm. Several warning signs can help spot when its time to swap or fix your shades - and spotting them early can help dodge some serious yet preventable health issues.

Unlike food, sunglasses don't come with a use-by date stamped on them. Instead, people typically get a few years' worth of wear from their glasses before the ultraviolet (UV) protection begins to deteriorate to a level where their eyes aren't as shielded from damaging UV radiation.

Eyewear maker Beautaste suggested that time alone isn't the problem. Inevitable things that lead to everyday wear and tear - including scratches, poor storage, and long UV exposure - all work together to make sunglasses less effective over time.

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Specialists advise that a decent pair of durable sunglasses can typically last "anywhere from two to five years, sometimes longer." But how long your beloved shades actually last will depend on how you wear, store, and maintain them, reports the Daily Record.

A 2016 study from the University of São Paulo recommended swapping UV-protective sunglasses every two years. However, this was based on the particular scenario of continuous, direct sunlight exposure (at least two hours daily, every single day, for 730 consecutive days) and most people don't use sunglasses in such harsh conditions - though the research does demonstrate the harm the sun's rays can inflict.

Sunglasses work by limiting the amount of visible light and harmful UV rays that reach your eyes. This is achieved through a combination of tinting, which absorbs light, and special coatings, such as UV filters, that block ultraviolet radiation.

Polarised lenses reduce glare from reflective surfaces like water or roads, improving visibility in bright conditions. This is particularly beneficial in situations where glare can be problematic, such as driving.

The National Eye Institute warns that exposure to UV radiation from the sun can lead to damage ranging from short-term conditions like photokeratitis (sunburned eyes) to long-term issues such as cataracts and age-related macular degeneration. To prolong the lifespan of your lenses, experts recommend storing them in a hard case when not in use.

Regular cleaning with a microfibre cloth and keeping them away from heat and direct sunlight are also advised. It's best to avoid placing them lens-down on hard surfaces to minimise the risk of damage.

When should you consider replacing your sunglasses?

If you notice scratches, cracks, or other visible damage to the lenses, it might be time to think about getting a new pair. If your eyes feel strained or more sensitive to light while wearing your sunglasses, this could indicate that they're no longer providing sufficient UV protection.

If you're fond of your sunglasses' style, swapping out the lenses themselves might be an option. The most efficient way to change your lenses is by visiting an optician who can choose the best lenses for your sunglasses and install them professionally, guaranteeing the lenses are fitted properly and continue safeguarding your eyes.

Certain sunglasses have removable lenses, making at-home replacement simpler. But, follow to the manufacturer's guidelines carefully to avoid damaging the lenses or the glasses themselves.

For those using this as a chance to update their style, specialists warn that costly and designer sunglasses aren't necessarily the best when it comes to health. Specsavers stated that buyers must be aware of "certified UV protection" to maintain eye safety from harm - and provided a guide on what to look for when choosing your next pair of shades.