You don’t have to climb Mount Everest or be in an arctic survival situation to become snow blind. You need only overexpose your eyes to intense UV light. Snow blindness can also happen indoors if you unwisely stare too long at welding work, or use a tanning bed without eye protection. The medical term for snow blindness is photokeratitis.
Photokeratitis occurs when the eye’s transparent outer layer that allows light into the eye, called the cornea, becomes sunburned. Like sunburns on other parts of your body, it takes several hours before you notice it. This means you can be enjoying yourself outdoors and not even know that you have already exposed your eyes to enough UV light to guaranty snow blindness in a few hours. Just like sunburn, snow blindness causes intense pain and will heal after two or more days. At this point, your vision returns.
Although eye pain and blindness should persuade most people to avoid UV exposure, consider that chronic exposure will cause serious eye conditions that may result in permanent blindness later in life. Each case of snow blindness also leaves you more vulnerable to getting the condition again.
How to Protect Your Eyes
You can protect your eyes by wearing sunglasses that provide 100% protection from both UVA and UVB. Don’t confuse lens tint with UV protection. A dark tint blocks visible light rather than UV, which is invisible to the human eye. A dark tint alone causes the pupils to dilate and allow more UV light into the eyes. Your glasses should either be made from a natural UV blocking material such as polycarbonate, or have a UV blocking coating applied.
Frame design also affects UV protection. UV light can enter the eyes from the top and sides of the sunglasses. If the frame is built for small lenses and/or doesn’t fit close to the face, then too much UV bypasses the lenses into the eyes and reduces the sunglasses’ effectiveness. Nike sunglasses have lenses that provide 100% UVA and UVB protection. The frames fit snugly to the face and allow for large lenses. One of the best frames available are the wraparound designs, which block UV entry from the sides.
Where to Use UV Protection
As mentioned previously, prolonged exposure to any UV light source will cause snow blindness. Some common outdoor recreational activities pose a severe risk. For example, skiing and snowboarding are often done at skiing centers in the mountains. UV radiation increases with altitude. You get an 11% increase in UV exposure for every 1000 meter gain in altitude. In addition, snow is a highly efficient UV reflector. It reflects up to 80% of UV light from the sun. This means the skier gets intense UV exposure from all directions.
A common reason for failing to wear sunglasses is forgetting to bring them. In this case, the skier or snowboarder should either end the activity or buy sunglasses from a shop at the ski center. The pain, blindness, and feeling of having sand in your eyes aren’t worth a few hours of recreation. Any outdoor snow activity carries this risk, including spending hours in the snow in your backyard.
Boating activities also carry this risk. Water is a good reflector of direct sunlight as well as UV backscatter coming from the sky. Note that polarized glasses doesn’t mean it blocks UV. Polarized lenses block visible glare, and unless the glasses are also UV rated, you won’t have protection.
Don’t expect the clouds to provide much UV protection, especially at higher altitudes. Even roofers, who spend hours in the sun, have suffered from this problem. In short, when you are outdoors, especially for long periods, wear your Nike sunglasses.