Leonardo da Vinci proposed a contact lens concept by placing the eye against a water-filled glass vessel.
In his Codex of the Eye, Leonardo explored how vision works and how the cornea affects the path of light. One experiment involved immersing the face in a bowl of water; another idea used a glass vessel filled with water placed directly before the eye. The arrangement anticipated the optical principle behind a contact lens by changing the interface in front of the cornea.
Leonardo did not create a modern wearable contact lens. His proposal was an optical experiment and conceptual forerunner, not a practical medical product that could be worn comfortably for long periods.
The idea is also distinct from spectacles, which sit in front of the eyes without touching the cornea. Modern contact lenses were developed much later using improved glass, plastics, manufacturing, and medical knowledge.