 Additionally, there are conditions such as keratoconus and aniseikonia that are typically corrected better with contact lenses than with glasses.Leonardo da Vinci is frequently credited with introducing the idea of contact lenses in his 1508 "Codex of the eye, Manual D", wherein he described a method of directly altering corneal power by either submerging the head in a bowl of water or wearing a water-filled glass hemisphere over the eye.Neither idea was practically implementable in da Vinci's time.