A Definition of Sight & Vision

For who does not know that the eye is a corporeal part of the head and that it is moist, and that it is that through which the sight pours forth from the brain like rays out of the meninx, that is, membrane. [The meninx, however, receives the nature of light from the heart, that is, from the seat of fire.] For sight is the emission of natural light in the sense of seeing of him who possesses it, bursting forth in the manner of rays, which, when it surrounds the colours and forms of sensible bodies without, with marvellous swiftness takes on the form [of those coloured visible shapes]. For vision is an image, formed in the rays of the eyes, of the shapes and colours of bodies, which with no intervening delay is seized by the sense and implanted in the memory of the percipient. It is the same with the sense of the ears. For that part of the head which is properly called ear is also called after hearing because it is the instrument of hearing ; and so it is for a thousand (other examples) of this kind.

Periphyseon, Book IV
The Definition of Sight
The Definition of Vision
John Scotus Erigena

“Humans see differently. They no longer see like us. Now their eyes can only take. They take in, they take notice of. Their eyes can no longer give. They’ve forgotten the light enters the heart through the eye… and then shines back out through the eye from the heart. The cycle is broken.”

Faraway, So Close!
Wim Wenders