Eye disorders caused by ultraviolet radiation
Sunlight effect on the eyes
Like so many other body parts, the eyes wear out with age and you can expedite the ageing process by allowing UV radiation damage. You will only notice the damage when it is too late though, when your vision is no longer good. And if you are very careless, you don’t have to wait that long: gazing at the sun can cause immediate damage.
The tissue at the front of your eyes absorbs most of the UV radiation, but at a cost. The tissue cells may alter their structure or become damaged, just like the skin cells do. While the skin has its tanning and dead skin cell layer as defences against radiation, the eyes don’t have this protection. They only rely on your eyelids to close. Unfortunately, because you can’t see UV light, the reflexes of closing your eyelids only work in combination with bright visible light.
Despite just a small percentage of UV light reaching the interior of your eye, it is still enough to slowly destroy some of the light-sensitive nerves on the retina. This is particularly true for the macula, the area of sharp vision (see ‘Macular Degeneration’). So, whenever you can, keep the harmful rays out by wearing UV-blocking sunglasses.
UV radiation damage can show itself in many forms:
- Degeneration. UV radiation accelerates the ageing process. Macular degeneration, the damage to the central part of the retina, is a leading cause of blindness in many countries. Degeneration of the cornea, droplet keratopathy, is common in populations in areas of high UV exposure.
- Sunburn. Sunlight can burn your eye as well as your skin. The cornea becomes inflamed and very painful (photokeratitis). While corneal injury is only temporary, a burn to the retina is permanent and affects the vision.
- Cataracts. Overexposure to UV light can cause clouding of the lens.
- Non-cancerous growth. UV radiation is said to trigger pterygium and pinguecula, fleshy growths in the corner of the eye. Normally both are harmless, but pterygium can invade the cornea and cause vision impairment.
- Cancer. Though rare, all types of skin cancer can affect the eye.
UV radiation damage to the eyes does not distinguish between races. The number of incidences is directly related to sun exposure. Recreational activities in snow, at the beach and on or near water, without adequate protection, increase the risk. Living and working in countries with high doses of UV radiation sees the numbers rise further.
Photokeratitis is the medical term for a sunburned eye and snow blindness. The front of your eyeball, the cornea, is subjected to high levels of UV radiation in mountain areas, on snowfields and on sandy beaches. Around two hours on snow and six hours on sand are enough to burn the eyes.
Unlike solar maculopathy, sunburnt eyes hurt. The pain can be severe but usually doesn’t occur until several hours later and a ‘snow-blind’ skier may blame the late night instead. Even the additional symptoms of red eyes, swollen eyelids, light sensitivity and blurred vision may not convince the person of the real cause. In any case, photokeratitis is not permanent. The affected eyes should fully recover within a few days.
Dry macular degeneration
You need the macula, the central vision, to read, write, drive and watch television. In other words, the macula provides you with the ability to see fine details. Macular degeneration is an irreversible damage to the light-sensing nerves. Don’t confuse this with farsightedness, which affects the lens and is easily corrected with reading glasses.
Age is the main risk factor in macular degeneration. One estimate puts the number of affected US citizens at approximately 10% of people in the 52 to 65 age group. Around half of the population over 75 has some form of macular degeneration. This number will rise with the overall increase in life expectancy.
Several other factors contribute to macular degeneration. The case against UV radiation, and most recently against blue and violet light, is continually strengthening. Bright light straight from the sun, or from reflective surfaces such as the ocean, snow or sand will ‘age’ the macula. It also doesn’t help to be a male smoker with a fair complexion, to be on certain medications, or to have parents and grandparents with macular degeneration.
The patient doesn’t lose vision completely, as the disorder doesn’t generally affect the peripheral and colour vision. But he or she will have a distorted or blank area in the centre of their vision, just like looking through spectacles with water droplets on their lenses’ centre. The droplets are clear at first but steadily become murky. This common ‘dry’ type of macular degeneration generally progresses slowly. An eye specialist often discovers these deposits before they affect the vision.
Wet macular degeneration
Much more serious and rapid is the ‘wet’ type of macular degeneration. Here, leaking and bleeding blood vessels grow underneath the macula, lifting it up and causing nerve cells to die.
The loss of vision can’t be repaired but certain precautions, such as UV radiation protection, improved fitness and a healthy lifestyle and diet can slow the progress. A surgical technique called laser photocoagulation may be able to destroy or block some of the leaking blood vessels before they become harmful. A new drug therapy aims for the same target. Also, some optical devices may help to shift the centre of vision to unaffected areas.
Does bright light bother you? If so, it doesn’t necessarily indicate a problem. Many people weep in bright sunlight, especially if reflective surfaces are present. If you visit an eye specialist, you probably experience light sensitivity afterwards if they have used some eye drops to dilate your pupils for the examination. As a result, more light can penetrate deep into your eyes, which is uncomfortable, sometimes painful, and may bring out some tears. Bright light is a trigger of migraine and headache in some people.
Light sensitivity, also called photophobia, is a common disorder and in some cases is the symptom of another problem. The light-sensitive person may have a medical disorder that triggers light sensitivity, or he or she reacts to certain drugs or toxins.