Though sunglasses may have been originally designed to dim the lights, today they do much more. Thanks to technology, sunglasses protect us from UV rays which can cause permanent damage to the vision. Here’s a rundown of what you need to know about UV and sunglasses.
What is UV light?
What we call “light” is a type of energy which flows in “waves” of different lengths, ranging from long, low energy rays of infrared (IR) to short, high energy rays of ultraviolet (UV). The human eye doesn’t see either IR or UV light but sees only the middle of the spectrum. Because of the high amount of energy it contains, UV light should actually be called “radiation.” UV radiation is responsible for skin damage caused by the sun, but the eyes are just as sensitive.
UVA, UVB and UVC
Radiation in the UV range can be split into categories from UVA to UVC, depending on wavelength and energy. UVC rays contain the highest amount of energy and would be most damaging, but virtually all of it is filtered out by our atmosphere. UVB rays are lower energy than UVC, but higher than UVA. UVB is partially filtered and is more concentrated closer to the equator. UVA rays are lower than UVB in energy but reach every place on the planet. Damage to living cells is caused by higher energy or longer exposure.
UV Rays and the Eyes
Everyone knows that overexposure to UV radiation causes sunburn, skin damage, increases the risk of cancer and can be blocked by sunscreen. Not as much focus is placed on the eyes, but it should be. UVA rays pass through the cornea to the lens and the retina. Over time, UVA exposure can contribute to cataracts and macular degeneration and may even lead to eye cancer. UVB damage can happen much more quickly. UVB rays can cause a “sunburn” on the cornea, known as photokeratitis. The most common example of this is “snow blindness” caused by extreme cornea and tissue inflammation, severe enough to cause blindness. This blindness may be temporary but in the worst cases, can lead to chronic irritation.
Sunglasses and UV Rays
In bright light the pupils provide some protection by constricting. On cloudy days however, more light is let through and UV exposure may be high. Using sunglasses that do not have UV protection could make UV exposure a greater risk. The first sunglasses were invented for comfort and did not block UV rays. Like cloudy days, wearing sunglasses could actually increase the amount of UV exposure.
The invention of the polarized lens in the 1930s made some UV filtering possible but the technology was expensive and did not provide total coverage, still many people think that better sunglasses must be more expensive. Today, a different technology is used to provide protection against UVA and UVB rays and is widely available at any price range. We no longer need to think that a high price, designer name, or darker tint provide more protection than an inexpensive pair as long as it says 100% UV protection.