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Wait and see.” It has long been a watchword of glaucoma management. Set a target pressure, then track the patient over time to see if the disease progresses. Tony D. Realini, MD, MPH, associate professor of ophthalmology at West Virginia University in Morgantown, calls it “clinical guesstimation.” If the patient progresses, you tweak the treatment to achieve a lower pressure, and then wait some more.
But following that approach is risky in patients with advanced glaucoma. In such cases, “tiny changes have an enormous effect on visual field and visual function,” said Dr. Realini. He explained that “in patients with early glaucoma, a 1 percent loss of visual function may mean a decrease from 90 to 89 percent, which doesn’t make much difference in terms of a patient’s abilities. There’s no margin for error when you’re down to your last 5 percent of visual function.”
The high stakes involved in managing patients with advanced disease are further raised by challenges particular to this patient population. Not only does advanced glaucoma elude definition, but, more important, the tests of function and structure that ordinarily guide treatment decisions are of diminished value in patients with advanced disease. Although some question remains on how best to preserve vision in these patients, experts agree that management differs significantly from earlier-stage glaucoma.
Defining and Monitoring
The experts say that there’s no standardized definition of advanced glaucoma.
Joel S. Schuman, MD, professor and chairman of ophthalmology at the University of Pittsburgh and director of the UPMC Eye Center, described the condition in objective terms as leaving patients with only a central and temporal island of vision, or even just a temporal island.
David C. Herman, MD, professor of ophthalmology at the Mayo Clinic in Rochester, Minn., offered a more subjective assessment. “If you feel the patient’s quality of life is at risk due to optic nerve damage in one or both eyes, then that would be a good working definition.”
“It’s like art,” Dr. Realini said. “We all know it when we see it.”
The limitations of standardized testing. The high-tech imaging that ophthalmologists typically rely on may be of little value in advanced glaucoma. In earlier disease, the nerve fiber layer serves as a measure of change, but when the NFL becomes quite thin, or very little of the neuroretinal rim remains, the information you get from these instruments is less useful, said Dr. Schuman. “It becomes harder, across the board, to detect change in people who have very advanced disease.”
And while it is possible to check visual fields by zooming in on the area of remaining vision with a Humphrey Visual Field 10-2, Dr. Schuman said, “Perimetry is not going to help in a patient with only a central or temporal island.”
He also pointed out the limitations of other testing methods. “A stereo disc photo or a visual exam is not going to tell you a lot about such a patient’s glaucoma, except that he or she has very bad disease. It’s hard to say whether vision is waning in terms of structural or functional testing,” Dr. Schuman said.
Listen to your patients. By that point, Dr. Schuman said, it’s the patient who will tell you that the disease is progressing. “They’ll tell you symptomatically,” he said. “They’ll say, ‘It’s getting darker.’”
The patient who notes a decline in activities such as reading and driving may help affirm results of ancillary functional and structural tests, said Louis R. Pasquale, MD, director of the glaucoma service and associate director of telemedicine at the Massachusetts Eye and Ear Infirmary. He urges clinicians to consider all possible means of detecting progression in advanced glaucoma, including patient complaints. “For the advanced glaucoma patient who performs poorly on formal visual field testing and who has anatomical features that make it difficult to monitor the disc, the treating physician may need to rely on the patient’s subjective complaints to detect progression,” said Dr. Pasquale. “The ‘How are you doing?’ test should not be discounted.”
“The inability to detect progression has treatment implications,” said Dr. Pasquale. “When does one intervene with invasive procedures when there are no objective criteria to show that visual function is getting worse?”
How low to go? Typically, patients with advanced disease need an IOP at episcleral venous pressure level, Dr. Pasquale said, adding, “Achieving such an IOP requires skill and luck.” He further noted that medications, laser trabeculoplasty and “blebless” glaucoma surgery almost never achieve the IOP levels required by patients with advanced disease. But lowering the IOP to less than 5 or 6 mmHg carries the risk of hypotony maculopathy. “Thus, the therapeutic window of IOP for the advanced glaucoma patient is quite narrow,” he said.
“There are no hard-and-fast rules here,” Dr. Pasquale added. “I would say when IOP creeps up above 15 mmHg and the patient subjectively feels that he or she is getting worse in the setting of clear media, one needs to consider more treatment.”
Dr. Realini agreed that there’s no consensus on treatment. “We don’t know how low pressure has to be in an individual. That target pressure varies from person to person and probably from eye to eye,” he said, adding that glaucoma may be asymmetric.
Adjusting target pressures. Dr. Schuman said that initially, you may set a target pressure based on population data, and later adjust the target pressure based on the patient’s progress. “But when the disease gets really bad and we’re not able to measure change, we have to go back to the population data and use that to help guide the treatment.” Those patients generally need quite a low pressure—12 mmHg or less—but even that may not be enough to control their disease. “If all you have left is a central island or just a temporal island, it’s important to ensure that the nerve is protected as much as possible by an IOP that’s going to be safe for that eye,” Dr. Schuman said.
The treatment dilemma. Yet some patients don’t need a pressure of 12, said Dr. Realini. The problem is, “We don’t know who those patients are.” And that’s the physician’s dilemma.
“Is more treatment always better than less? We’re torn between treating everyone very, very aggressively, knowing we may be overtreating some, with consequences,” Dr. Realini said. Alternatively, you can wait and see. “But then there may be a handful of patients who need a lower pressure and progress.” The physician, he said, has to choose between possibly harming the patient from overtreating or from undertreating. “That’s a rotten place to be.”
Dr. Realini’s approach. “I hedge my bets,” he said. Because the risk factors for surgical complications are generally different from the risks of disease progression, he typically operates on only one eye. “With one eye operated on and one eye not, now we have two different sets of risk factors for blindness. Either eye might go blind,” but the statistical odds for going blind in both eyes are low, he said. “It’s a reasonable combination of aggressive and conservative management.”
Glass half full. “There will likely be some patients who go blind no matter how low we get the pressure,” Dr. Herman said. In a retrospective, community-based study he coauthored, patients who had optic nerve damage at the time of diagnosis had a 27 percent probability of going blind in one eye, and a 16 percent probability in both eyes, over a mean follow-up of 15 years, beginning in 1965.1
The good news is that the probability of going blind from glaucoma may not be as high as it was for the patients in Dr. Herman’s report. “We now have much better tools that are more sensitive and specific to detect change and many more medical and surgical options,” Dr. Herman said. “The onus is upon us to do a better job.”
Making the most of what remains. Even when a patient loses vision, the ophthalmologist still has important work to do. “When we say that a patient with advanced glaucoma has gone blind, we generally don’t mean no light perception. Functionally, patients often become significantly limited at the level of 20/400 or beyond, when limited to counting fingers,” Dr. Realini said. “But the function they retain is of enormous importance to them and to us. We’re still trying to save what bit of visual function they have.”
1 Hattenhauer, M. G. et al. Ophthalmology 1998;105(11):2099–2104.
Drs. Herman, Pasquale and Realini report no related financial interests. Dr. Schuman receives royalties for intellectual property that is owned by MIT and licensed to Carl Zeiss Meditech.