The Eye

The eye is covered by a firm layer, the sclera. Within the sclera you find the choroid, which is continuous with the ciliary body and the iris in the front part of the eye. The pupil is formed by a hole in the iris. The inner part of the eye is covered by a photosensitive layer, the retina. The optical system also comprises the cornea, the lens, the vitreous body of the eye and the aqueous humor, a chamber filled with fluid.

Incoming light is focused on the retina by the lens. The photosensitive cells of the retina, the photoreceptors, are stimulated by light and then produce signals which are pre-processed by other nerve cells in the retina and transmitted by the optic nerve to the visual cortex of the brain. This is where the signals are transformed into a visual perception.