In 1950, University of Innsbruck professor Theodor Erismann used a pair of custom goggles to turn the eyesight of his student, Ivo Kohler, upside down.
After ten very difficult days, Kohler began to see the world as normal. Above is video from the experiment.
"The impressive abilities of our perception" (Universitat Wurzburg)
"Experiments show we quickly adjust to seeing everything upside-down" (The Guardian, 2012)
(via Weird Universe)