Tes Vov Iyar, 5773
You are sitting in the Heichal Halimmud studying a Ma'amar with a Chavrusa when, suddenly, you hear a "clink," coupled with a sudden inability to see the words on the page clearly. What just happened? One of the lenses of your glasses has fallen out! You had realized it was a bit shaky in the morning, but figured you'd take care of it later. Now you have no choice but to interrupt your shiur and get it fixed.
Although this is a typical experience, if this occurs on a Shabbos, it poses more of a problem. For someone with a high prescription, waiting until Motzei Shabbos to replace the lens is not easy. He may have great difficulty Davening, learning, and even recognizing his friends for the rest of the day.
A double question then arises: May the lens be put back into the frame on Shabbos? If not, may one hold the lens to the eye to aid his eyesight until it can be replaced?