We are often asked why we specifically require “Glacier Glasses” on our climbs, rather than regular sports sunglasses. The answer to this questions is best understood with a bit of background knowledge regarding the effects of a high altitude snowy environment on the solar radiation to which you are exposed.
Altitude and Solar Radiation
Lots of us spend large amounts of time in the sun at low elevations with minimal negative effects. However, as soon as you begin to ascend to higher altitudes, there is less atmosphere to filter dangerous ultraviolet rays, and solar radiation increases significantly. According to the World Health Organization, “a thinner atmosphere [at altitude] filters less UV radiation. With every 1000 meters increase in altitude, UV levels increase by 10% to 12%”.
Additionally, the snowy environment we so often find ourselves in while mountaineering (glaciers, snowfields, etc.) can reflect up to 90% of the solar radiation that hits the surface, meaning that the sun’s radiation hits you not only from the sky, but also from the ground. These factors together mean that the effective intensity of UV solar radiation can be more than double that of sea level at 3000m (9800’).
Increased exposure to these UV rays can cause both temporary and permanent damage to our eyes, including photokeratitis (snow blindness), erythropsia, cataracts, and corneal burns. This is why we take eye protection seriously in the mountains!
‘Normal’ sports sunglasses allow for between 60 and 30% Visible Light Transmission (VLT). Proper glacier glasses, on the other hand, will fall somewhere in the 5-7% VLT range, in addition to providing close to 100% frame coverage (no light can sneak into your eyes from the bottom or sides of the sunglasses frame), meaning your eyes will be much better protected than in a standard sunglasses frame. For those who wear prescription lenses, prescription glacier glasses are available from Julbo USA or Opticus (over-the-glasses models can work for shorter trips, but prescription lenses are preferable for expedition use).
While lots of options exist in the marketplace for glacier glasses, you’ll want to make sure any eyewear you’ll be taking into the mountains has excellent frame coverage, a secure fit, and <10% VLT (for high altitude expeditions, look for 5% VLT). As long as you follow those tips, your eyes will remain happy and healthy in the mountains, allowing you to safely experience the world’s highest places!