The human eye gives us more information about the outside world than any other sensory organ, producing continuous images that are instantly transmitted to the brain for processing. Not only is the eye a personal window on the world, but it offers a noninvasive and immediate view into the body's vascular system, providing physicians with an opportunity for early diagnosis of hypertension and diabetes.

In an adult, the eye has a diameter of approximately 25mm (or one inch). It sits in a cavity in the skull called the eye's orbit. The one sixth of the eye's surface that is exposed beyond the orbit is protected against strong light and foreign objects by the eyelids, eyelashes, and eyebrows.

The outermost layer of the eyeball is the visible white of the eye, the sclera, which provides structure and strength; it is covered by a thin membrane called the conjunctiva.