How can I convince girl to take off gles during ?

My new girlfriend wears gles and the thing is that when we have she won't take them off. I am afraid to tell her cause she might get mad. I have been a little nearsighted since middle school and never wear gles. I can drive, read, I work, and do everything without need for gles. So how come she can't take them off when she's with me? I think she would look even better without them.