ABSTRACT
The eyeball is lined with light-sensitive neurons. At the front of the eye, the cornea allows light into the eye and refracts that light. The eye has two chambers separated by a lens. Contraction or relaxation of the ciliary muscles determines the shape of the lens, and therefore the focusing of the eye. In front of the lens is the iris, that controls the amount of light reaching the retina. Contraction of the annular muscle reduces pupil size, while contraction of the radial muscle dilates the pupil. Pupil diameter is controlled largely by the autonomic nervous system.
