The eyeball

Recently we started talking about the eyeball and all of its parts and its functions. There are three layers to the eyeball. The outermost layer is called the sclera. The sclera is what forms the white part of your eye. On top of the sclera is the conjunctiva. This is a thin clear covering that helps to protect your eye. It also is a lining on the inside of your eyelids. Also on the outermost layer is the cornea. The cornea is another transparent layer that allows light to enter into the eye. The cornea, together with the lens helps focus and direct light onto the retina.

The next, or middle layer is called the Choroid. It is a membrane found between the sclera and the retina, it lines the back of the eye. It contains many blood vessels that supply oxygen and nutrients to the retina, and is highly pigmented to help absorb light and prevent scattering.

The innermost layer is the retina. The retina lines the inside of the back part of the eye, and is the light-sensitive part. The retina contains millions of cells known as photoreceptors, and each photoreceptor is linked to a nerve fiber. You have a blind spot, also known as the optic disc, at the back of each eye where all of these nerve fibers come together to form the optic nerve. Once an image is detected by the photoreceptors, this information is converted into nerve impulses that are sent to the brain through the optic nerve.

The iris of the eyeball sits right on top of the ciliary body. The iris is the colored part of our eye. The black circle in the center of the iris is called the pupil and it is actually a hole.

There are six small muscles of the eye. The superior oblique is the muscle the moves the eye inward and downward. The lateral rectus moves the eye outward (away from the nose). The medial rectus is the muscle that allows you to cross your eyes (move eyes toward your nose). The superior rectus is what makes the eye moves the eye upward and slightly out. The inferior rectus moves the eye down and slightly inward. The sixth and final muscle of the eye is inferior oblique moves the eye outward and upward.