What Is Glaucoma?

WHA T IS GLA UCOMA ? SARAS RAMANATHAN and J. TERRY ERNEST* After studying the more than 150 years of research in glaucoma, one is struck by the magnitude of what is still not known. In an ideal world, a physician might be confronted by a patient who, after being newly diagnosed with glaucoma, asks his doctor, "What is glaucoma ?" She would answer with confidence that glaucoma is an eye disease in which there is progressive and irreversible damage to the optic nerve that is often but not always associated with high intraocular pressure. She would go on to explain that due to the damage to the optic nerve, there is characteristic loss of peripheral visual field. The main treatment goal in glaucoma is to lower the eye pressure to an acceptable level so as to prevent that damage to the optic nerve. Having said all of this, she would start her patient on a topical medication to lower the intraocular pressure, give him appropriate reading material on glaucoma and schedule his follow-up appointment . But of course, one does not practice in an ideal world. The Real World Instead, this is a world in which half of all Americans with glaucoma are undiagnosed. Almost 2 million Americans have glaucoma, and it is the leading cause ofvision loss among African Americans, and the second leading cause of blindness among Americans overall [I]. Glaucoma is often a difficult disease to recognize. Patients with glaucoma may have eye pressures that range from high to low and may have varying damage to the optic nerve. This in turn may or may not correlate with loss of peripheral visual field. For example, a typical patient may have a highnormal intraocular pressure, may exhibit characteristic glaucomatous change to the optic nerve, but may have normal peripheral visual field. *Department of Ophthalmology and Visual Science, University of Chicago, 939 E. 57th Street, Chicago, IL 60637. The authors wish to gratefully acknowledge the diligence of Sandra Wallace, for her assistance in preparation of this manuscript.© 1998 by The University of Chicago. Ail rights reserved. 0031-5982/98/4201-1077$01.00 8 Ramanathan and Ernest ¦ What Is Glaucoma ? Does this patient have glaucoma? Or does he have ocular hypertension with unusual appearing optic nerves? Perhaps he has some sort oí forme fruste glaucoma. Does his physician commit him to a lifetime of eye drops in a presumed effort to prevent eventual glaucomatous vision loss? Or does she wait until the patient loses visual field before starting treatment? Since the answers to such questions may be very difficult, the physician usually chooses the route ofgreatest caution. She follows the patient closely under the diagnosis of "ocular hypertension" or "glaucoma suspect" until the glaucoma declares itself more fully, or until she is convinced that the patient does not indeed have glaucoma at all—just a few red herrings. Fortunately, as the subject of glaucoma is often frustrating, today's ophthalmologists find that they are in good company. For over 100 years, ophthalmologists have been trying to find answers to seemingly unanswerable questions. What is glaucoma? How is it related to high eye pressure? What is the mechanism of glaucomatous visual field loss? How can we effectively distinguish those patients who will eventually develop glaucomatous vision loss? What is the most effective treatment? Historical Perspectives STARTING OFF ON THE WRONG FOOT Characteristically, the glaucoma patient has always been something of a mystery to the ophthalmologist. Three hundred years ago, a patient with high eye pressure and resultant corneal edema presented to his eye doctor. The physician ofthat era, recognizing the decreasedvisual acuity and opacification of anterior structures of the eye, made the diagnosis of "glaucoma ." Unfortunately, the term glaucoma actually means opacification of the lens, or cataract. So, in fact, not onlywas the very early glaucoma patient misdiagnosed, but the very term glaucoma is an erroneous appellation. It seems ironic that a disease that is still somewhat inscrutable to ophthalmologists had it origins in a cloud of misconception. THE PROBLEM OF PRESSURE Itwas not until the 1830s that William McKenzie described an "abnormal hardness" to the eyes [2] . This was followed by the groundbreaking discovery in 1851 by Hermann von Helmholz...