It's weakness is quite simple, Just have the eye look at your sword and move it in a circular motion until it gets confused and shuts its eye. It will then fall off the door and die. It may also come in different variations - two-eyed and three-eyed. For multiple eyes to become dizzy at once, Link must stand in a location fit to have all eyes focus on his pointed sword at one time. Attempting to single an eye out will be negated, since they are tied together and must be deattached together.