your eyes get a good showering of UV rays with or without sun glasses. The light spills through the gaps between your lens and face.
Having said that ski and swimming goggles are pretty excellent, except they don't breath as well as cycling glasses.
Personally I use a specialized ArcTerra... fits my face pretty good with minimal leakage, lenses get darker when it's brighter... comes with a lifetime warranty too, which I dig.
Now I just worry about swallowing bugs, or bugs getting caught in my atmos vents...