The eyepatch is an anti-piracy measure designed to punish people who pirate the game. In pirated versions, you are forced to wear it for the whole game. In the real game, you can turn it off and on at will.
When you wear the eyepatch, It will obscure half of the screen, and all slimes will turn into parrots who can not only fly, but their plorts are bird droppings. The bird droppings have a default value of 1.
radioactive fat exploding parrots lol