I can't believe my eyes!

Excellent! You've found the right answer.
Glasses which are thicker in the middle compared to its edges are called converging lenses. Such lenses focus or converge the light rays and reduce the focal distance of our eyes. People like Michael's grandpa, who have difficulties with reading and with seeing close by objects, have an eyeball which is too short and clear images are created behind the retina. This vision disorder can be compensated with the help of a converging lens.