Glaucoma
Medical Author: Lawrence J. Schwartz, MD
Previous Medical Editor: Leslie J. Schoenfield, MD, PhD
Medical Revising Author: Camille Hylton, MD
Medical Revising Editor: William C. Shiel Jr., MD, FACP, FACR
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Save Your Sight - Glaucoma ScreeningMedical Author: Melissa Conrad Stöppler, MD
Medical Editor: Barbara K. Hecht, PhD  Glaucoma is the term applied to a group of eye diseases that gradually result in loss of vision by permanently damaging the optic nerve, the nerve that transmits visual images to the brain. The leading cause of irreversible blindness, glaucoma often produces no symptoms until it is too late and vision loss has begun.
An elevation in the pressure within the eye (the intraocular pressure, or IOP) is generally, but not always, associated with the development of glaucoma, although additional factors are also likely to play a role in its development. The optic nerve fibers inside the eye are damaged, resulting in vision loss that begins in the peripheral fields of vision. Glaucoma usually affects both eyes, but one eye may be more severely affected than the other. |
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What is glaucoma?
Glaucoma is a disease of the major nerve of vision, called the optic nerve. The optic nerve receives light from the retina and transmits impulses to the brain that we perceive as vision. Glaucoma is characterized by a particular pattern of progressive damage to the optic nerve that generally begins with a subtle loss of side vision (peripheral vision). If glaucoma is not diagnosed and treated, it can progress to loss of central vision and blindness.
Glaucoma is usually, but not always, associated with elevated pressure in the eye (intraocular pressure). Generally, it is this elevated eye pressure that leads to damage of the eye (optic) nerve. In some cases, glaucoma may occur in the presence of normal eye pressure. This form of glaucoma is believed to be caused by poor regulation of blood flow to the optic nerve.
How common is glaucoma?
Worldwide, glaucoma is the leading cause of irreversible blindness. In fact, as many as 6 million individuals are blind in both eyes from this disease. In the United States alone, according to one estimate, over 3 million people have glaucoma. As many as half of the individuals with glaucoma, however, may not know that they have the disease. The reason they are unaware is that glaucoma initially causes no symptoms, and the loss of vision on the side (periphery) is hardly noticeable.
What causes glaucoma?
Elevated pressure in the eye is the main factor leading to glaucomatous damage to the eye (optic) nerve. Glaucoma with normal intraocular pressure is discussed below in the section on the different types of glaucoma. The optic nerve, which is located in back of the eye, is the main seeing nerve for the eye. This nerve transmits the images we see back to the brain for interpretation. The eye is firm and round, like a basketball. Its tone and shape are maintained by a pressure within the eye (the intraocular pressure), which normally ranges between 8 and 22 mm (millimeters) of mercury. When the pressure is too low, the eye becomes softer, while a too high pressure causes the eye to become harder. It turns out that the optic nerve is the most susceptible part of the eye to high pressure because the delicate fibers in this nerve are easily damaged.
The front of the eye is filled with a clear fluid called the aqueous humor, which provides nourishment to the structures in the front of the eye. This fluid is produced constantly by the ciliary body, which surrounds the lens of the eye. The aqueous humor then flows through the pupil and leaves the eye through tiny channels called the trabecular meshwork. These channels are located at what is called the filtering, or drainage angle of the eye. This angle is where the clear cornea, which covers the front of the eye, attaches to the base (root or periphery) of the iris, which is the colored part of the eye. The cornea covers the iris and the pupil, which are in front of the lens. The pupil is the small, round, black-appearing opening in the center of the iris. Light passes through the pupil, on through the lens, and to the retina at the back of the eye. Please see the figure, which is a diagram that shows the filtering angle of the eye.
Legend for figure: This diagram of the front part of the eye is in cross section to show the filtering, or drainage angle. This angle is between the cornea and the iris, which join each other right where the drainage channels (trabecular meshwork) are located. The arrow shows the flow of the aqueous fluid from the ciliary body, through the pupil, and into the drainage channels. This figure is recreated from Understanding and Treating Glaucoma, a human anatomy board book by Tim Peters and Company Inc., Gladston
