Sunglasses have an expiry date: how often do they need to be renewed?

If you've been wearing the same sunglasses for years, maybe it's time to change them, because yes, sunglasses do expire. Use and external agents such as heat can deteriorate lenses. If they are scratched or have lost part of their protective film (you will see halos on the lenses), they will allow ultraviolet rays to pass through, which can cause damage to both the crystalline lens and the macula of the eye.

One of the most common effects is photokeratitis, with symptoms such as intense eye pain, a sensation like something is stuck in the eye (like sand), tearing, sensitivity to light, blurred vision and redness.

How often should they be replaced? It depends on how you use and care for them, as well as what type of glasses you have. According to ophthalmologists, glasses usually expire between three and four years after you start using them. For this reason, experts recommend annual ophthalmological check-ups to assess both the patient's eyes and the condition of the glasses they wear.

Doctors also have some tips for maintaining sunglasses in optimal conditions. They recommend storing them in a case, preferably a hard-cover one, especially if they are going to be used sporadically; cleaning the lenses with specific products or with a neutral soap, always using a cloth for this purpose (never paper); and not leaving them exposed to external agents such as the sun, as well as making sure that they do not bend.

There is no point in complying with the aforementioned recommendations if sunglasses are not approved from the start. As the Andalusian regional ministry of consumer affairs has recently reminded us, "these items are considered personal protective equipment (PPE), as their lenses protect us from damage caused by ultraviolet radiation". For this reason, the regional department has stated that they should be purchased in authorised and trustworthy establishments - such as opticians' shops - and "never on the street".

To make sure that the sunglasses are approved, look at the labelling, which should show both the CE marking and the reference to ISO 12312. The type of filter (polarised, photometric or gradient) and the filter category indicating the level of glare protection, among other information, should also be listed. There are five categories for sunglasses, from 0 to 4.

Those included in category 0 are intended for situations of very low solar luminosity. Their use is more aesthetic or for comfort for indoor or semi-covered spaces, cloudy days or low light.

Category 1 is for low light conditions, suitable for urban use.

Category 2 includes glasses with lenses designed for medium brightness, suitable for sunny days or for sports such as running or cycling.

Category 3 provide high protection in conditions of strong luminosity, recommended for use on the beach or in the mountains.

Finally, Category 4 sunglasses offer very high protection against glare and are designed for very bright conditions and for use in high mountain sports such as skiing and water sports. The regional ministry has stated that glasses of this category are not allowed while driving vehicles.

For daily use in an urban environment, ophthalmologists recommend sunglasses with protection level 3, as they filter out 90% of ultraviolet radiation and reduce the impact of rays on white surfaces such as sand, water or snow in winter.