Are your sunglasses healthy glasses?

Looking into the bright sun doesn’t feel good. The tissues in the eyes are much more sensitive to sunlight than the skin. But where our skin can’t protect itself, our eyes can. The pupils get smaller in a lot of sun and limit the light that can penetrate into the eyeball; we peer through our eyelashes and when we are totally blinded, we just close our eyes. That happens all by itself, an innate automatism. Under normal light conditions you therefore do not necessarily need sunglasses.

However, the situation changes when you are behind the wheel of the car or hiking through the mountains. Closing your eyes is no longer an option. At such a moment, sunglasses are not an unnecessary luxury, but an important tool to continue to see well or to protect against sunburn.
Because just like the skin can also burn the eyes. Anyone who has been in the bright sun for half an hour to a few hours will suffer from burning eyes. That can lead to photokeratitis, popularly called welding eye or snow blindness. The outermost cell layer of the eye, the cornea, is then burned. The whites of your eyes often look a bit red and it feels like there is sand in the eye. Sometimes this feeling is so intense that you can hardly open your eyes or tolerate light. Fortunately this will pass. The doctor prescribes some eye ointment and after a night’s sleep the worst of the damage is over.

The invisible culprit

The culprit is the UV light, the ultraviolet radiation. This UV light is invisible, you cannot see how much UV is in the air. But when the sun is visible, there is often a lot of ultraviolet radiation. Heat doesn’t matter much; on a cool sunny day in summer there can be just as much radiation as there is in tropical temperatures. The position of the sun does matter. In summer, the sun is high in the sky (closest to Earth) and the amount of UV radiation increases. The radiation is strongest at half past two in the afternoon. Even if you have your eyes closed, it’s best to have a sunglasses to wear. Even if it’s just to protect your eyelids, which are usually not rubbed.
KNMI continuously measures the sun’s power, the amount of UV rays that reach the earth. On teletext (708) or on knmi.nl you can see if there is a risk of burns.

What makes UV light so different from visible light? You could see light as a vibration. Visible light gives very slow vibrations, invisible light vibrates so fast that we cannot see it. The disadvantage of these fast vibrations is that they can penetrate deeper into the tissues, where they can cause damage. This causes your skin to burn and skin cancer can originate.
UV light comes in three varieties: UV-A, UV-B and UV-C. The difference lies in the wavelength of the vibrations, from long to short. Fortunately, we don’t have to worry about UV-C, which is blocked by the ozone layer. But UV-A and UV-B cause the aforementioned snow blindness and can probably also cause other problems for the eyes in the long term. Probably because it’s hard to prove. An eye disease like macular degeneration (damage to the yellow spot) develops gradually and researchers never know exactly how much light a person has had in their life.

Doesn’t it help…

Still, there is some evidence that persistent too much light could lead to stare (clouding of the lens of the eye). People in the tropics get cataracts ten years earlier than people in a temperate climate. But the chance that you will develop cataracts at some point in your life is high: a third of people over 85 suffer from this eye disease.
A pterygium also seems to be related to UV radiation, because it is more common in people who live in a sunny climate. In this eye disease, the conjunctiva, which normally sits on the white of the eye, grows over the cornea in a triangular shape. This can irritate and in the worst case the tip of the triangle grows over the pupil, obstructing the view. Whether you can really prevent these diseases by wearing sunglasses is therefore questionable. On the other hand, if it doesn’t help, then it doesn’t hurt. And you may reduce the risk a bit.

It’s a different story if you already have an eye disease and therefore find it difficult to tolerate light. This is called photophobia, although it is not strictly speaking a phobia. You are not afraid of light, but it can hurt if too much light hits the eyes. This is not a disease in itself, but a symptom that can occur in eye conditions such as iridocyclitis (inflammation of the iris), acute glaucoma (excessive pressure in the eyeball) and uveitis (inflammation of the choroid), as well as meningitis, albinism and migraine. For these people, there are sunglasses that allow only a small percentage of light through and also block the light from the side.

The Older Eye

Is it still important to protect your eyes later in life? Is there still something to win? Yes, protection also remains important for people over 50. You may already have something wrong with your eyes; a small additional damage can quickly deteriorate your condition.
Moreover, the influence of UV light on the older eye is different from that on a young eye. Normally, the cornea and the lens of the eye filter a large part of the UV radiation from the light. In young people, therefore, only 1 percent reaches the retina. The older, the more irregular the lens structure becomes, causing scattering of light and UV radiation. As a result, the light bounces in all directions and the retina ages extra quickly. However, on the other hand, the lens turns more yellow and therefore allows less light to pass through.

Thanks to Tjeerd de Faber, ophthalmologist at the Rotterdam Eye Hospital.