Through the action of small muscles (called the ciliary muscles), the lens becomes thicker to focus on nearby objects and thinner to focus on distant objects. By changing its shape, the lens focuses light onto the retina. The size of the pupil is controlled by the action of the pupillary sphincter muscle and dilator muscle.īehind the iris sits the lens. Thus, the pupil dilates and constricts like the aperture of a camera lens as the amount of light in the immediate surroundings changes. The iris allows more light into the eye (enlarging or dilating the pupil) when the environment is dark and allows less light into the eye (shrinking or constricting the pupil) when the environment is bright. The iris -the circular, colored area of the eye that surrounds the pupil-controls the amount of light that enters the eye. The cornea serves as a protective covering for the front of the eye and also helps focus light on the retina at the back of the eye.Īfter passing through the cornea, light travels through the pupil (the black dot in the middle of the eye).

Light enters the eye through the cornea, the clear, curved layer in front of the iris and pupil.

The conjunctiva also covers the moist back surface of the eyelids and eyeballs. Near the front of the eye, in the area protected by the eyelids, the sclera is covered by a thin, transparent membrane ( conjunctiva ), which runs to the edge of the cornea. The outer covering of the eyeball consists of a relatively tough, white layer called the sclera (or white of the eye).

Split pupil into 2 diseaes