The eye of an adult measures about one inch from the front to the back of the eye; a child's eye measures about three-quarters of one inch.

The eye has three layers:

1- Sclera - the outer protective white coating of the eye

2- Choroid - the middle layer which contains blood vessels to nourish the eye

3- Retina - the inner layer which contains the nerves that bring information to the brain for seeing

The cornea is the clear portion of the front of the eye which bends light rays. The conjunctiva is a thin tissue which lines the eyelids and the eyeball up to the edge of the cornea. The iris is the colored portion of the eye which is made up of a spongy tissue and is an extension of the choroid. The pupil is the opening in the iris (black) which allows light into the eye. The lens helps focus light rays onto the retina the way a camera lens focuses light onto film; the lens can change shape, or accommodate, to focus on near or distant objects.

The eye is filled with fluids which help nourish and maintain the pressure within the eye. The anterior chamber, the front portion of the eye between the iris and the cornea, is filled with aqueous humor, a watery fluid which nourishes the lens and mantains the pressure within the eye. The back portion of the eye is filled with vitreous humor, a transparent gel.

The retina is made up of ten layers and contains over one million cells. The optic nerve has nerve fibers which transmit information to the brain for interpretation of objects seen.

The macula is the area of the retina that is responsible for central vision; its central portion is referred to as the fovea and is responsible for the sharpest vision. The macula houses the highest concentration of the cones which are responsible for color and sharp vision. The rods, which compose the rest of the retina, are more sensitive to light and are responsible for night vision and peripheral vision. Attached to the globe of the eye are six muscles which aid in the movement of the eye. Movement of the eye may be caused by one, a few, or all of the muscles working together.


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