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The anatomy of the eyeball allows humans and other animals to see the world around them. This organ is specially designed to process light that is either emitted from or reflected off of objects. Though many animals have the ability to see in very low levels of light, the anatomy of the eyeball does not allow it to function in the complete absence of light. Specialized cells and structures in the eyeball are responsible for the sense of sight.
The front of the eyeball is covered by a clear membrane known as the cornea. This membrane allows light to enter, while keeping foreign bodies from entering the eyeball. An opening in the front of the eye, known as the pupil, contracts and expands allowing the eyeball to admit more or less light. The anatomy of the eyeball in humans includes a round pupil, though the pupil may be square or elliptical in other animals.
Once light enters the eye, it forms an upside-down image on the back of the interior of the eyeball, the retina. This structure is covered by specialized cells known as rods and cones. Rods process light, while cones allow the eyeball to sense color. The information collected by the retina leaves the the eyeball, enters the brain through the optic nerve, and is processed into a visual image.
Aside from the components of the eyeball that allow for light to be processed, there are various other systems included in the anatomy of the eyeball as well. Many muscles around the outside of the eyes allow the eyeball to move with great precision and accuracy. The muscles are so sophisticated in many animals that a quickly moving object can be kept directly in the center of the field of vision while the head is turning and even while the body is in motion.
The eyeball also requires a supply of blood and vitamins in order to keep the organ functioning properly. The retinal artery, which enters the eye through the back, along the same channel as the optic nerve, is the only source of blood and nutrients for the eyeball. The eyelids, and in some animals the nictitating membrane, are parts of the anatomy of the eyeball that protect this sensitive organ from damage.