I first started shaving without my glasses when I forgot to take my glasses to the gym, where I most often shave. I am short sighted but have no problem distinguishing between the white of the lather and the pink of my skin. I actually found it helped not being able to see as well, like it made me worry less about being perfect.
On a side note, when I was younger and tried rock climbing it was less scarry and therefore easier, to climb with a blind fold. I feel it is a similar situation with shaving. But of course I would never shave with a blind fold (if some one is willing to try, it would make a great video for utube).