I don't know I've never paid much attention, maybe it's cause I need glasses or contacts to see or I couldn't even see what your question said and I'm sitting in front of a 24" monitor lol. Glasses or no glasses important thing is she can see me and not walk into walls or street signs.
I personally find glasses to be very attractive on a woman, for what reason that is I do not know. I suppose it is a 'Turn on' or something of that nature. Though this differs from man to man. Maybe it could be that intellectuals tend to wear glasses and a woman wearing glasses gives off the impression she is such.
Why should it matter if a girl has a visual impairment? I have a hearing impairment and I wear a hearing aid in my left ear. "Do you prefer a girl who can hear or one who doesn't understand a word your saying?" is basically the same as "do you prefer a girl who can see or a girl that walks into walls?"
It's what's on the inside that matters, you're beautiful no matter what impairment/disability you have :)