New York-Structure does predict function, George A. (Jack) Cioffi, MD, told participants in the Glaucoma 2004 meeting here, and therefore measurement of the optic nerve head is important in assessing the presence and progression of the disease.
Dr. Cioffi, chairman, Devers Eye Institute, Legacy Health System, Portland, OR, was one of three speakers at the meeting's first session, Detecting Structural Damage in Glaucoma. He was preceded by David S. Greenfield, MD, who emphasized the importance of clinicians recognizing the fundamental characteristics of the glaucomatous optic nerve (GON).
"Cup-to-disc ratio is an extremely important and descriptive term, but when one describes and documents the characteristics of the GON, it is critical to recognize other structural characteristics," said Dr. Greenfield, associate professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami, FL.
"An alteration of these typical relationships, often with thinning of the inferior portion of the neural rim, increases suspicion of early glaucomatous optic nerve damage," Dr. Greenfield said. Application of the rule can also help assess progression of glaucoma, he added. These descriptive features of the optic nerve are extremely subtle and occur slowly over time; changes can be detected using periodic stereoscopic optic disc photography.
Dr. Cioffi's presentation focused on the SAFE (Structure and Function Evaluation) study, in which 479 eyes of 295 patients were evaluated over 4 years. The structure of the optic nerves was examined periodically with stereophotographs of the optic nerves and by scanning laser tomography.
All the patients had been evaluated for the presence of glaucomatous optic neuropathy before the study began. All had elevated IOP and normal visual fields at baseline. Over the course of the study, 272 eyes developed glaucomatous visual field loss, and the great majority of them, 75% to 80%, had GON at the start. Fewer than 10% of the eyes without GON converted to glaucoma, Dr. Cioffi said.
In addition, examination of the retinal nerve fiber layer (RNFL) holds greater promise for measuring progression of glaucoma than for early detection, Dr. Cioffi said. Ideally, a diagnostic test would distinguish completely between the normal eye and one that is in the process of becoming glaucomatous. This is not now possible, he said, because of the wide variation between individuals. Thus, there is no clear-cut line that can be drawn to distinguish between the normal eye and one that will develop glaucoma, but a series of measurements can track the progression of the condition. Therefore, monitoring progression of the disease will likely be where optic nerve head analysis will be of the most benefit.