Heh Ootomo Megane must really have a glasses fetish or something to draw two girls keeping their glasses on while having sex. I hate falling asleep with my glasses on and waking up to them smooshed in my face, so I can't even imagine keeping them on while getting up close and personal with someone.
I dunno, my girlfriend and I keep ours on (tho I tend to wear contacts more often than not). We're both extremely nearsighted, so it's nice to be able to see each others' faces from a distance, y'know, for quality control of intimacy.
I love Megane's work, there's something quite beautiful in how he draws faces.