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Health Effects of Ozone Depletion: Eye Disorders

Introduction

Ozone's unique physical properties allow the ozone layer to act as our planet's sunscreen, providing an in visible filter to help protect all life forms from the Sun's damaging ultraviolet (UV) rays. Most incoming UV radiation is absorbed by ozone and prevented from reaching the Earth's surface. Without the protective effect of ozone, life on Earth would not have evolved the way it has. The ozone layer protects us from the harmful effects of certain wavelengths of ultraviolet (UV) light from the Sun. The danger to our eyes from ultraviolet radiation comes mainly from the UV-B range of the spectrum, although UV-A poses some risk if exposure is long enough. Any significant decrease of ozone in the stratosphere would result in an increase of UV-B radiation reaching the Earth's surface, and of eye disorders.

UV-B and Eye Disorders

UV-B radiation can damage the cornea leading to photokeratosis or "snow blindness", and can also cause cataracts through damage to the lens and the retina.

Strong UV radiation can cause inflammation of the cornea leading to photokeratosis or "snow blindness". Symptoms of this kind of an infection include the eyes becoming reddish, a sensitivity to light, enhanced excretion of tears, the feeling of having some dirt in one's eye, and pain. The trauma appears 3-12 hours after exposure. Thanks to the quick regeneration of the eye cells, symptoms will normally disappear within a few days. A long-term exposure to UV radiation may cause permanent damage to the cornea.

UV radiation also enhances the dimming of the eye's lens, which means that potential cataracts begin to evolve at earlier ages. A cataract is a partial or complete opacity of the lens of the eye and the largest cause of blindness in the world. Part of the UV radiation reaches the back of the eye, causing cells in the retina to slowly begin to deteriorate. Damage will in time particularly occur to near vision. If not operated upon blindness can occur. Radiation is partly absorbed in the lens of an adult eye, but will go right through the lens of a child, reaching the back of the eye. For this reason, children's eyes in particular should be protected against strong sunlight.

Other common eye diseases associated with increased UV-B radiation are eye cancer, conjunctivitis and pterygium. Conjunctivitis is an inflammation of the membrane covering the anterior portion of the eyeball. Pterygium is a thickening of the membrane that covers the eyeball.

Ozone Depletion and Eye Disorders

As the ozone layer gets thinner, UV-B radiation at the surface of the Earth increases. If the ozone amount decreases by 10% during the spring and summer, the annual UV dose increases by about 12%.

Cataracts and blindness are among the most common eye diseases associated with further ozone layer depletion and increased UV-B at the Earth's surface. Unlike the skin, which can adapt to UV radiation by becoming browner and thicker, the eye does not have any such defence mechanisms. On the contrary, research shows that eyes become more sensitive with increased exposure to radiation. This can damage the cornea, the lens and the retina.

Increased exposure to UV radiation from ozone depletion is expected to increase the number of people experiencing cataracts. A 1% decrease in stratospheric ozone may result in 100,000 to 150,000 additional cases of blindness due to eye cataracts world-wide.