In the mountain, sunlight coming from above and in front is not always a big deal. It all boils down when it is reflected off of the surface of snow. Most prescription mountaineering glasses are usually wrap around so that they can provide maximum protection from UV rays’ penetration.
Usually, UV protection is the number one selling point when purchasing the best mountaineering glasses. Scientifically, UVA rays penetrate deep into the dermis, which is the skin's thickest layer. Unprotected exposure can lead to premature skin aging and wrinkling (photo-aging), and suppression of the immune system. UVB rays will usually burn the superficial layers of the skin. It plays a key role in the development of skin cancer. Even though weak, UVC can cause Erythema.
Apart from wrapping around the face, prescription mountaineering glasses should be certified category 3 and 4. Category 3 & 4 glacier sunglasses offer 100% protection against UVA and UVB radiation. Inevitably, the most important part of one’s body when taking part in mountaineering is the eyes. One needs their eyes as functioning properly as much as they need the legs to move through the snow.
The damage caused by the light that glares from sunlight is fatal. It can either cause instant blindness or delayed irritation which shows up a few days after getting exposed.