From a non-medical perspective, “snow blindness” is visual impairment and intense pain caused by over-exposure to bright light and ultraviolet radiation reflected off the snow. In our Clothing main section, Head Gear and Eyewear subsection, we have described how important proper eyewear is for traveling over snow in winter. We cannot overemphasize enough how important quality sunglasses and goggles with UV protection are for prevention of eye damage.
If you have never had snow blindness and you are not using eye protection, it may take a while to creep up on you after a long day of intense exposure to reflected light off snow. After a long day your eyes will have severe pain and tearing, and you may be visually impaired and unable to expose your eyes to medium or intense light for a day or more. Obviously not a good thing to let happen on a trip, especially considering your long term vision health. UV is ionizing radiation and can cause eye disease.
I have had too much unprotected exposure to UV over the years, and I now suffer intense snow blindness symptoms with an onset in a matter of seconds if the sun comes out and I am out traversing open lakes covered in snow. Even overcast days may bring on symptoms immediately without eye protection. The symptoms include extreme pain, the inability to keep eyes open, and profuse tearing which blurs vision. To prevent this I use UV blocking glacier glasses (with Rx lenses), with the side shields to block incoming radiation from the side as well. I carry an extra pair of sunglasses in my day pack too. Glacier glasses also work as light wind goggles, so I can’t say enough good things about them.
When it is very cold and you have to wear face protection such as a face mask, eye glasses and sunglasses often fog up, and you will have to do without glasses and switch to ski goggles with UV protection. Or you may have to use the goggles anyway to seal up the skin around your upper face from frostbite. Luckily I can see reasonably well without my Rx glasses, but if you have poor vision, this fogging problem is a significant handicap. I purchased the ski goggles specifically specially sized big to fit over eye glasses (ask for them in your local ski shop). Sometimes I can battle the eyeglass fogging inside the goggles, but sometimes nothing seems to work. Please let us know if you have found an effective anti-fogging formula for glasses when wearing either face masks or goggles. Its one of the holy grails of winter travel for us eyeglass wearers.
Should you ever be caught without sunglasses and its bright out, you can rig a set of Inuit style ice goggles with a piece of birch bark. Make thin slits for eye holes and rig with a piece of cord. You may need spacer blocks of something to hold the goggles out from the face. If you have more time, you could whittle a pair out of softwood.