What optical device did Leonardo da Vinci study as a model of how the eye forms images?

Leonardo da Vinci studied the camera obscura as a model of how the eye forms images.

A camera obscura is a darkened room or box with a small opening through which light enters. The opening projects an inverted image of the outside scene onto an interior surface. Leonardo used the device to investigate vision, light, perspective, and the structure of the eye.

His notebooks contain detailed observations comparing the camera obscura with the human eye. He understood that the image entering through the pupil is inverted, and he explored how the eye and brain nevertheless produce a useful view of the world. These studies linked practical optics with anatomical research.

Leonardo did not invent the camera obscura. Ancient writers, including Mozi and Aristotle, described related optical effects, and later artists used the device for drawing. Leonardo’s contribution was his sustained investigation and his detailed explanation of the analogy between the optical box and the eye.