Ocular Anatomy
The
structure of the eye is similar to that of a simple camera. The
cornea and lens in the front of the eye act together to focus light
much like the lens of a camera focuses light. The iris, which is
similar to the diaphragm of a camera, opens and closes to adjust the
amount of light entering the eye. The eyeball itself is hollow, and
the inside of the eye is filled with a clear gel called the vitreous
humor. The image is focused onto the retina, which is the back of the
eye. The retina, which is analogous to film in a camera, is a thin,
nerve layer that lies on the back, inner wall of the eyeball. The
retina is made up of nerve fibers and cells called photoreceptors.
There are two types of photoreceptor cells: rods and cones. The rods
can detect low amounts of light, which is useful for night vision.
The cones are used to detect colors. These photoreceptors convert the
light image into electrical signals which are carried by the nerve
fibers centrally into the optic nerve and then to the brain. The
macula is the central area of the retina 
which
is the part most important for vision. Most of the photoreceptors of
the retina are located in the macula. The macula is the part of the
retina that is responsible for seeing straight ahead, for seeing
color, and for performing fine visual tasks such as reading. Any
damage to the macula will result in problems with vision.
The retina has its own blood supply, which comes in from behind the eye and centers the retina through the optic nerve. A single artery (the central retinal artery) brings the blood into the retina and a single vein (the central retinal vein) drains the blood out of the eye as it makes it way back to the heart.