The Structure of the Eye¹¹Yanoff M, Duker JS. Ophthalmology. 1st ed. London, UK: Mosby International Ltd; 1999.

In order to better understand what glaucoma is and how medications are used to treat it, you need to know a little about the basic structure of the eye.

To make eyesight possible, light and its resulting nerve impulses must pass through several structures in the eye. Use the illustration on the right to view each part of the eye as follows:

• Cornea The healthy cornea is transparent and smooth; its curved surface helps to admit and channel light into the pupil.
• Sclera Known as the "white of the eye", the sclera is a rigid coating that gives the eye its shape. It is opaque to exclude light.
• Iris When we identify the color of our eyes, we are referring to the color of the iris. The iris muscles contract and relax to allow less or more light into the eye as needed.
• Pupil The pupil is the opening (hole) that grows larger or smaller when the iris expands or contracts. Light travels through the pupil to the lens.
• Lens The lens is transparent and changes shape to focus light rays on the back of the eye. This allows us to see objects at a range of distances.
• Retina The retina is the tissue that covers the inside of the eye. The retina has a layer of nerve fibers that absorb light and transmit sensory information to the brain for processing.
• Optic Nerve The optic nerve is the bundle of nerve fibers and cells from the retina. In the center of the optic nerve bundle are the major blood vessels that carry blood to and from the retina and choroid.