At the same time, German medical student August Muller was experimenting with glass discs aimed at improving vision-his own, actually. His 1889 thesis recounts that although he could get the lenses fit on his eyes, violent pain kicked in about a half an hour after insertion. But with the short-lived fix, his myopia improved.
Two things to keep in mind about these early glass models: First, the lenses were huge. They were not the small, light things we have today. Instead imagine big glass sheets—about twice the size of current disposables—blanketing even the whites of the eyes. The shape exacerbated problem number two. Glass was the wrong material. Eyes need to breathe. ...
For these reasons, very few people—maybe 500 in the world, estimates Efron—wore early models. Eyes would tolerate, at most, four hours of air-prohibiting abuse. It wasn't until 1948, when optical technician Kevin Tuohy realized by accident that contacts didn't have to cover the whites of the eyes at all, that wearers were allowed some extra hours. While Tuohy was lathing the lens, a recently invented transparent plastic, the part supposed to cover the whites of the eyes dropped off. This left him thinking, Is there a way the smaller lens could actually work? So he polished down the disk's edges and tried the slimmer model himself. To his surprise, it actually stayed put—even after blinking.
--Rachel Swaby, Gizmodo, on an innovation that is obvious after the fact