Contact lens
The contact lens is a fictitious invention, created on April Fools' Day as a joke by Douglas Adams of Hitch-hiker's Guide to the Galaxy fame.
A parody of the Babel fish which when inserted into the ear allows its wearer to understand any language except legalese and COBOL, the contact lens would supposedly be inserted into the eye to help one see.
The premise is evidently nonsense; how on earth is someone expected to see if they have something in their eye?
Nonetheless a coalition of optimists, ophthalmologists and opticians have perpetuated this classic myth, largely because its famed author somehow lends it a modicum of undeserved credibility in much the same way that Plato's tales lend an aura of credibility to the famed myths of Atlantis and New Atlantis.
No one has ever seen a contact lens, despite many wasted hours searching for the blasted things, so most observers have dismissed the legends as mere fiction. Some credulous onlookers nonetheless continue to believe in this mythical invention and dismiss the many sceptics as being merely short-sighted.