Leonardo da Vinci described an early contact-lens concept using a water-filled glass sphere.
In the Codex of the Eye, Leonardo discussed placing the eye in contact with water inside a glass vessel. The arrangement was intended to alter the way light entered the eye and to explore how vision works. Later accounts often identify this proposal as an early conceptual ancestor of the contact lens.
Leonardo did not create a practical modern contact lens. His apparatus was large and experimental, and there is no evidence that people routinely wore it as a corrective device. The first successful practical contact lenses were developed much later, using glass and then plastics designed for safer, more comfortable wear.
The idea is also distinct from spectacles, which sit in front of the eyes without touching them. Leonardo’s proposal is remembered because it recognized that changing the optical surface directly at the eye could affect vision, a principle central to contact lenses today.