How does Juror #6 offer an insight when #4 removes his glasses?

When the 4th Juror rubs his nose where his spectacles have made indentations, the 9th Juror realizes that the woman also had those same marks on her nose and must have worn glasses, despite the fact that she didn’t wear them in court, presumably for her own vanity. This causes all of the jurors to question the eyesight of the woman, who may have witnessed the murder without her glasses.