Warmth
Goggles, which fit closes to the forehead and form a seal, are inherently warmer than wearing glasses. Goggles also do a much better job at keeping wind from bothering your eyes because of the tight fit.
Vision
Goggles have better peripheral vision than sunglasses do. With goggles, you can also get ones that have interchangeable lenses. Though the expense of interchangeable prescription lenses can be great, it also lets you match the right lens tint to the lighting conditions, so that on overcast, stormy days, which have very flat light, you can still see contours in the slope.
Fogging
Even though some goggles do a better job than others at ventilation and preventing fog and moisture buildup, the seal that makes them warmer than sunglasses makes them inferior to sunglasses for ventilation. If you fall a lot and tend to fog up your goggles, sunglasses should be seriously considered.
Construction
While prescription sunglasses can be made from glass, polycarbonate is a better choice for impact resistance. Prescription sunglasses for sports should also have flexible ear pieces to make securing them easier. Goggles are always made from polycarbonate.
