The eye is the visual organ of the human body. It is a complex organ, designed to focus light through the front portion of the eye (cornea), through the midportion of the eye (lens), onto the back portion of the eye (retina).

A cross section of the eye shows three basic layers of tissue. The outer layer is a white, tough, protective layer called the sclera. This white layer of the eye is readily visible to observers. The cornea is made of similar tissue to the sclera, but it is transparent and is important in focusing light into the eye. The middle layer of the eye is the uvea, or uveal tract. This layer provides blood flow and nutrition to the eye. The inner layer of the eye is the retina. It is a very delicate transparent layer, measuring only approximately 200 microns in thickness.

The retina is light sensitive and provides sight for the eye. The retina is comprised primarily of nerves and blood vessels that exit the eye at the optic nerve. The optic nerve leads directly to the brain.

The uvea is subdivided into 3 anatomic portions termed the iris (anterior part), ciliary body (middle part), and choroid (posterior part). The uvea is comprised of blood vessels and pigmented cells called melanocytes. Primary malignant melanoma of the uvea generally originates from the melanocytes (pigment cells). It if occurs in the iris, it is called iris melanoma, whereas if it is in the back of the eye in the choroid, it is called a choroidal melanoma.