Spending time out in the sun can put your eyes at risk for damage that can lead to cataracts, macular degeneration, and other serious vision problems. Knowing what factors affect the strength of UV rays can help you protect yourself from eye and skin damage from the sun.
UV or ultraviolet radiation is a non-visible part of the light from the sun. UV rays are generally divided into two types: UV-A and UV-B. Both types of UV radiation cause damage to the cells in the body that can lead to skin and eye damage. Any time the sun is shining, whether you can see it or not, UV radiation is present. But the amount of UV radiation varies depending on a number of factors:
• Time of Day – The sun is at its highest point each day around noon. This means UV rays are traveling the shortest distance through the atmosphere and are strongest between about 10 am and 2 pm. Early morning and late afternoon sunlight has a lower risk of UV exposure.
• Time of Year – The angle of the sun changes during different seasons of the year. UV radiation is strongest in the summer and weakest in the winter.
• Setting – UV levels can vary depending on your surroundings. UV radiation is higher in open spaces, especially when there are reflective surfaces including sand or snow. Light reflecting off snow can have nearly double the UV risk, and can cause snow blindness. Tall buildings that provide shade can reduce UV exposure.
• Latitude – The sun is more directly overhead at the equator. This means UV rays travel the shortest distance through the atmosphere, which makes them stronger at the equator. The farther away from the equator you go (closer to the north or south poles) the weaker the UV radiation becomes.
• Altitude – How far above sea level you are affects UV rays. The higher you are, the thinner the atmosphere is above you to absorb harmful rays. UV intensity is stronger at higher altitudes. So if you live in or travel to the mountains, take extra precautions to protect your skin and eyes.
• Weather – If the skies are cloudy it may seem as though you are safe from UV exposure. That is not the case. Heavy clouds can reduce UV levels. But UV damage is still possible depending on the thickness of the cloud cover.
• Ozone – The ozone layer is part of the earth’s atmosphere that absorbs most of the damaging UV radiation from the sun. Chemicals such as car emissions have caused thin spots in the ozone which allow more radiation to pass through. Other factors including time of year and weather also affect the thickness of the ozone layer. Scientists take the thickness of the ozone layer into account when calculating the UV index for any particular location.
In addition to these natural UV risk factors, certain medications can increase your body’s sensitivity to UV radiation. Take extra care to protect yourself from UV rays if you are taking tetracycline, sulfa, birth control pills, diuretics, or tranquilizers.
The UV index is a standard scale that measures the intensity of UV radiation. Knowing the UV index in your area can help you plan appropriately to protect your skin and eyes. The U.S. Environmental Protection Agency offers a tool to calculate the UV index by zip code. The agency also offers mobile UV apps for web, Blackberry, and Android to help you track the UV index during the day.