(Homonym: I, aye).
The organ of sight ('peeper' is an informal term for 'eye'); SYN. oculus, optic, peeper.
The organ of vision. In the human eye, the light is focused by the combined action of the curved cornea, the internal fluids, and the lens. The insect eye is compound—made up of many separate facets—known as ommatidia, each of which collects light and directs it separately to a receptor to build up an image. Invertebrates have much simpler eyes, with no lenses. Among mollusks, cephalopods have complex eyes similar to those of vertebrates.
The mantis shrimp's eyes contain ten color pigments with which to perceive color; some flies and fishes have five, while the human eye has only three.
This is a roughly spherical structure contained in a bony socket. Light enters it through the cornea, and passes through the circular opening (pupil) in the iris (the colored part of the eye).
The ciliary muscles act on the lens (the rounded transparent structure behind the iris) to change its shape, so that images of objects at different distances can be focused on the retina. This is at the back of the eye, and is packed with light-sensitive cells (rods and cones), connected to the brain by the optic nerve.