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n. the organ of sight: a three-layered roughly spherical structure specialized for receiving and responding to light. The outer fibrous coat consists of the sclera and the transparent cornea; the middle vascular layer comprises the choroid, ciliary body, and iris; and the inner sensory layer is the retina (see illustration).

Light enters the eye through the cornea, which refracts the light through the aqueous humour onto the lens. By adjustment of the shape of the lens (see accommodation) light is focused through the vitreous humour onto the retina. In the retina light-sensitive cells (see cone, rod) send nerve impulses to the brain via the optic nerve. The arrangement of the two eyes at the front of the head provides binocular vision. Each eye is contained in an orbit, and movement of the eye within the orbit is controlled by extrinsic eye muscles (see illustration).

Extrinsic muscles of the left eye.

The eye (sagittal section)

Subjects: Medicine and Health — Literary Studies (Early and Medieval).

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