Sure - but how do you know? If the pax knows that gaining an exit row seat is dependent on them answering the question "Is the correction on your glasses less than N?" with YES, then they will. If you don't want to check hearing and eyesight at the check-in desk, then make a simple blanket ruling.
But even if you did, I'll bet there are folks who would take their glasses off first and lie through their teeth. Sorry if that sounds harsh but paxing for 40+ years can leave a jaded feeling about travellers ...