Designer sunglasses are aimed mainly at the younger market, but they are more than a mere fashion statement, they can play an essential role in protecting the eyes.
Eye care is of increasing importance the older you get, and the elderly can be more prone than most to eye problems, especially those related to exposure to ultraviolet (UV) rays.
Health experts have warned for years about the danger of bright sunlight to the skin and of the need to wear high factor sunscreen.
But the eyes need shielding too as UV radiation can not only damage the lens surface but can penetrate to much deeper levels.
Different types of lenses for sunglasses
Sunglasses come in all styles, colours and shapes these days and they come in all kinds of material too, from high-tech acetates to commonplace wood, paper and even bamboo.
Fortunately, most modern sunglasses come with lenses that offer 100% protection from harmful UV light.
The key to protecting the eyes against harsh sunlight is blocking light waves of a particular wavelength; this is sunlight in the UVA and UVB bands of 380 to 400 nanometres.
It is a common fallacy to think that darker lenses block more UV light. Lenses that are entirely clear can still stop UV light reaching the eyes, and the best guide to their efficiency is on the label.
How sunglasses can help the elderly
Eyesight tends to get worse with age, and many older people report blurred or limited vision which can worsen as the years roll by.
Regular and prolonged exposure to sunlight can contribute to some of the problems. The most common are irritation of the cornea, known as keratitis, and clouding of the lens caused by cataracts.
Cataracts are a prevalent eye problem for the elderly, and the impact of excessive sunlight is a factor in the growth of this condition.
Age-related macular degeneration, a common cause of blindness in the elderly may also be linked to the exposure of eyes to high-energy UV light rays.
Avoiding sunlight altogether is not recommended as that can exacerbate other health problems but blocking UV rays with good sunglasses is a simple, and stylish, way to minimise sun damage.
When to wear sunglasses
Sunglasses can be worn when outdoors in pretty much any kind of weather and, as long as they have 100% UV protection the elderly can be sure their eyes are safe.
It's important not to confuse UV protection with other types of lens. Polarised lenses, for example, will cut down glare, especially from horizontal reflective surfaces, but polarisation in itself will not stop UV rays reaching the eyes.
Similarly, polychromic lenses will darken as the light gets brighter, but again, there is no inherent UV protection here. It's even the same with mirror coated lenses; they may reflect lots of light, but the light that gets through may still contain harmful UV rays.
That is not to say that lenses with special coatings are not beneficial for good eyesight. They can improve vision dramatically, sharpen contrast and enhance colours but they have no effect on UV light penetration.
Of course, special coatings can be used in conjunction with lenses that already offer 100% UV protection so you can get the best of all worlds, but it's important not to confuse them.
Danger of sunglasses for the elderly
Another word of warning here. The old need to take care when walking out of doors as a slip or fall can cause severe damage so they should take great care that the sunglasses they choose do not limit perception.
Mirror lenses, for example, reflect lots of light and, although they look cool on the outside, they keep the wearer very much in the dark.
In the same way, coloured lenses can alter true colours and warp contrast enough to make wearing them a hazard for older people.
Polychromic lenses too, do not change shade immediately and stepping from a dark room into the sunlight and vice versa can cause temporary problems until the lenses 'adjust' to the new conditions.