The eye has three main layers. These layers lie flat against each
other and form the eyeball.
The outer layer of the eyeball is a tough,
white, opaque membrane called the sclera (the white of the eye). The slight
bulge in the sclera at the front of the eye is a clear, thin, dome-shaped
tissue called the cornea. See a picture of the
The middle layer is the choroid.
The front of the choroid is the colored part of the eye called the iris. In the
center of the iris is a circular hole or opening called the pupil.
The inner layer is the retina,
which lines the back two-thirds of the eyeball. The retina consists of two
layers: the sensory retina, which contains nerve cells that process visual
information and send it to the brain; and the retinal pigment epithelium (RPE),
which lies between the sensory retina and the wall of the eye.
The inside of the eye is divided into three sections called
Anterior chamber: The anterior chamber is the front
part of the eye between the cornea and the iris.
The iris controls the amount of light that
enters the eye by opening and closing the pupil.
The iris uses
special muscles to change the size of the pupil. These muscles can control the
amount of light entering the eye by making the pupil larger (dilated) or
Posterior chamber: The posterior chamber is between
the iris and the lens. See a picture of the
iris and lens.
The lens is behind the iris and is normally
clear. Light passes through the pupil to the lens.
The lens is held in place by small
tissue strands or fibers (zonules) extending from the inner wall of the
The lens is very elastic. Small muscles attached to the lens
can change its shape, allowing the eye to focus on objects at varying
Tightening (contraction) or relaxing these muscles
causes the lens to change shape, allowing the eyes to focus on near or far
Vitreous chamber: The vitreous chamber is between the
lens and the back of the eye.
The back two-thirds of the inner wall of the
vitreous chamber is lined with a special layer of cells (the retina): millions
of highly sensitive nerve cells that convert light into nerve
Nerve fibers in the retina merge to form the optic nerve,
which leads to the brain. Nerve impulses are carried through the optic nerve to
The macula, near the center of the retina at the back of
the eyeball, provides the sharp, detailed, central vision for focusing on what
is in front of you. The rest of the retina provides side (peripheral) vision,
which allows you to see shapes but not fine details.
(retinal artery and vein) travel along with the optic nerve and enter and exit
through the back of the eye.