What is it?
Glaucoma is an eye disease in which there is gradual damage to the nerve fibers of the optic nerve. This nerve registers what we see by connecting the retinal ganlion cells to the vision center in brain. Usually, but not always, the damage of glaucoma results from elevated pressure inside the eyeball.
A liquid called the aqueous fluid (also called the aqueous humor) fills the anterior and posterior chambers of the eye, and is responsible for nourishing the lens, iris, and inner cornea. The amount of this fluid determines the pressure within the eye. The animated illustration on this website, circulation of aqueous fluid, shows that the aqueous fluid is produced and secreted by a structure called the ciliary body, circulates through the chambers, and then drains out of the eye and into the venous circulation via a maze called the trabecular meshwork, which is located in the angle formed where the iris and the cornea intersect. Deficiencies in this outflow system (particularly in the trabecular meshwork) can raise the intraocular pressure (IOP).
Primary open-angle glaucoma (POAG) is the most common form in US. It usually affects people over age 40, and blacks are much more suscepible than whites. About three million Americans have the disease, and half of them don’t know they have it. An estimated 80,000 people in the US are legally blind, in both eyes, from glaucoma. It is the principal cause of blindness among blacks, and the second-leading cause (after age-related macular degeneration) of blindness in the whole American population. Much of this suffering could have been prevented by early detection and treatment of the disease. There is widespread ignorance about glaucoma. Many people think that it is painful or that it is caused by high blood pressure; both of these statements are false, and can lead to a false sense of security.
Symptoms
Glaucoma is silent. There is no pain in POAG and no changes in vision at first, even though the optic nerve is slowly being damaged. This is why there is a great need to diagnose the disease early, before there is any loss of vision. Glaucoma is the best example of a the serious eye disease for which early detection really helps, because there are effective treatments that will prevent or slow down vision loss. In later stages of the disease, if it is not treated, there is a gradual, bilateral loss of peripheral vision; this means that you fail to see objects that aren’t right in front of you. Gradually the field of useful vision gets smaller and smaller.
The glaucoma animation shows what the world might look like to a person with progressive symptoms of glaucoma.
Prevention
Glaucoma cannot be prevented. However, if it is detected early, before there is vision loss, it can be controlled. The aim is to keep as many as possible of the 100,000 retinal ganglion cells in each eye alive and healthy; these are nerve cells and cannot replenish themselves. Therefore, vigilance is the key. Everyone should have his or her intraocular pressure checked by an ophthalmologist or optometrist at age 40, and regularly thereafter. The instrument the doctor uses to measure pressure is called a tonometer. But this is not enough because, in many cases of glaucoma, the pressure within the eyeball is not elevated. You should get a thorough eye exam, through dilated pupils, according to schedule given in “obtaining eye care”. Your eye-care professional will look for optic-nerve “cupping” and changes in the appearance of the retina and the retinal blood vessels. If anything looks abnormal, the doctor will measure the extent of your visual field by a painless method called perimetry.
People with a family history of glaucoma, blacks, diabetics, and people who are either very nearsighted (high myopes) or who are taking steroids on a long-term basis, are at much higher risk of developing glaucoma. The overall prevalence of POAG in the US is about one percent, but in black populations it has been reported to range from two to nine percent. Therefore, if you are in any of these categories, you should get complete eye examinations more frequently, starting at a younger age, in order to get treatment before permanent damage is done.
Treatment
There is no cure for glaucoma, and any vision lost to the disease cannot be brought back. However, prescription eyedrops can often control the disease by lowering eye pressure (IOP). Some drops act by decreasing aqueous fluid formation; others help the fluid leave the eye more efficiently. These eyedrops, plus medicines in pill form, are usually the first method of treatment used. The drops and pills often are effective in delaying (and sometimes even preventing) optic-nerve damage. If medications do not help enough, laser surgery may be employed to stretch the channels in the trabecular meshwork and increase drainage of fluid out of the eye. If these methods do not control the progress of glaucoma, conventional surgery may be necessary, to make a new opening for fluid to leave the eye.
Research at the Schepens
Several groups at the Schepens are investigating various aspects of glaucoma:
Studies of the effect of pressure on cultured cells taken from the optic nerve head.
Mechanisms of rescue of retinal ganglion cells, by growth factors, after experimental optic-nerve injury in a mouse model. Dr. Dong Feng Chen.
Development of a mouse model of pigment dispersion glaucoma. Dr. Wayne Streilein.
Low-vision aids are available for people who have sustained considerable and irreversible loss of their visual field due to glaucoma, and who want to lead as normal a life as possible. These devices may allow people to read, watch TV, and in some cases, even drive. See Eli Peli's website, information from the National Eye Institute, and two other websites: www.lowvision.org and www.lowvisioninfo.org.
For more information about glaucoma, see the NEI website and their information page on glaucoma