Eyeworld

MAR 2012

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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110 EW GLAUCOMA February 2011 March 2012 Is normal tension glaucoma different from primary open-angle glaucoma? by Tony Realini, M.D., M.P.H. episode," he said. "Also look for clues on examination such as the angle, central corneal thickness, and evidence of old burned-out pigmen- tary glaucoma." "Not every patient with sus- pected normal tension glaucoma needs to be worked up," he said. "Instead, a workup should be re- served for those patients in whom the clinical findings don't necessar- ily fit glaucoma." These include patients whose visual field defects tend to respect the vertical meridian, those whose optic nerves are more characterized by pallor than cupping, those with color vision defects, and younger patients, he said. In these patients who don't fit Source: Coneyl Jay/The Image Bank/Getty Images Specialists debate the differences T he very existence of normal tension glaucoma has been debated for decades. Is it simply primary open-angle glaucoma within the nor- mal portion of the IOP spectrum, or is it a separate disease with a distinct clinical appearance? EyeWorld reopens the door on the discussion that a panel of experts had regarding the potential differences between normal tension glaucoma and high tension open-angle glaucoma at the 2011 annual meeting of the Ameri- can Glaucoma Society in Dana Point, Calif. Clinical differences "I think normal tension glaucoma is a distinct entity," said Joseph Caprioli, M.D., chief of glaucoma, David Geffen School of Medicine, University of California, Los Ange- les. "Eyes with normal tension glau- coma look different and behave differently from eyes with high ten- sion glaucoma." In normal tension glaucoma, he said, the optic nerve is more likely to have disc hemorrhages and beta- zone peripapillary atrophy than in high tension glaucoma. "Also, nor- mal tension glaucoma is character- ized by deeper, steeper defects on visual field testing that are more commonly closer to fixation than high tension glaucoma." The rate of progression may also distinguish these two entities. "Nor- mal tension glaucoma may progress more often and more rapidly than high tension glaucoma," he added. Evaluation In the absence of elevated IOP, the decision whether or not to embark on an extensive workup for pre- sumed normal tension glaucoma patients is a common clinical dilemma. "The patients that we worry about most are those in whom we don't have high IOP to blame for their disease," said Gregg Heatley, M.D., associate professor, ophthal- mology and visual sciences depart- ment, School of Medicine and Public Health, University of Wisconsin, Madison. "In these patients, consider his- torical issues such as past steroid use or a remote hypovolemic shock the glaucoma mold, he said, the workup might include things such as lab tests and orbital imaging. "Also, in light of data suggesting a link between sleep apnea and normal tension glaucoma, it might be worthwhile to consider polysomnography, a sleep study to detect obstructive sleep apnea," he said. Potential pathophysiology "In glaucoma, we are concerned about pressure," said Stuart McKinnon, M.D., associate profes- sor, ophthalmology and neurobiol- ogy departments, Duke Eye Center, Duke University, Durham, N.C. "But what pressure should we be measur- ing? The primary site of damage in glaucoma is the retinal ganglion cell axon at the level of the lamina cribrosa. So why are we measuring pressure at the cornea if we're con- cerned about the optic nerve head?" He pointed out that there are two circulating fluid compartments that meet at the lamina cribrosa and said that perhaps what we should be more concerned about is translami- nar pressure, which is calculated as the difference between intracranial pressure (ICP) and IOP. It may be that the absolute level of IOP makes better sense in the context of ICP, he explained. "Several recent studies have demonstrated that ICP is signifi- cantly lower in both normal and high tension glaucoma compared to healthy controls," he said, "while in ocular hypertension, ICP is higher than in controls." In addition, he said, ICP de- creases by as much as one-third after age 50, "which is the age group in which we most often see glaucoma," he said. "Therefore, it is possible that translaminar pressure is a rele- vant parameter in the pathophysiol- ogy of glaucoma." Treatment issues Once the diagnosis of normal ten- sion glaucoma is made, the next de- cision is whether and how to treat the patient. "The Collaborative Normal Tension Glaucoma Study showed convincingly that patients do better if you lower IOP," said George A. "Jack" Cioffi, M.D., chairman, Devers Eye Institute, Portland, Ore. "But when I make treatment deci- sions on my patients with normal tension glaucoma, I find it useful to consider the patient in terms of a therapeutic window." The therapeutic window is a bal- ance between the risks of treating and the risks of not treating, he ex- plained. "An example of a wide ther- apeutic window is a young patient who is progressing with a relatively high IOP—say, 20 mm Hg—on no medications. In this patient, the benefits of treatment far outweigh any risks. There is no compelling reason not to treat. "In contrast, consider the older patient with a remote history of an intracapsular cataract surgery with delayed secondary lens implanta- tion, who is now progressing with an IOP of 11 mm Hg on two medica- tions. There is less room to maneu- ver with this patient. The likelihood is that the patient will require sur- gery to halt progression, and that comes at great risk in this eye. "The narrower the therapeutic window," he said, "the less likely I am to enter it." EW Editors' note: The doctors interviewed have no financial interests related to this article. Contact information Caprioli: caprioli@ucla.edu Cioffi: jcioffi@deverseye.org Heatley: gheatley@wisc.edu McKinnon: stuart.mckinnon@duke.edu

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