Eyeworld

EW GLAUCOMA 49 A study suggesting that re- duced cerebrospinal fluid pressure (CSFP) is a risk factor for glaucoma has triggered a series of inves- tigations to better understand the significance of this novel observa- tion. The current thinking is that the pressure differential across the lamina cribrosa—termed the translaminar pressure—may explain why some eyes are more susceptible to glaucomatous optic neuropathy at seemingly low IOP, while others seem impervious to elevated IOP. The theory is that within a healthy range, translaminar pressure is appropriately balanced between IOP and CSFP and the lamina re- mains in a stable configuration, thus protecting the axons passing through it. If an unhealthy translaminar pressure gradient de- velops, the lamina can be deformed, compromising axonal support. "CSFP may act as a counterbal- ance to IOP by decreasing the pres- sure gradient present at the optic nerve head," said John Berdahl, M.D., Sioux Falls, S.D. Dr. Berdahl was the lead investigator of the group that first reported the rela- tionship between CSFP and glau- coma. "The translaminar pressure is defined by both IOP and CSFP," ex- plained David Fleischman, M.D., University of North Carolina at Chapel Hill, and a member of the re- search team. "Therefore both ele- vated IOP and low CSFP could increase the risk of glaucomatous optic neuropathy." The research team responsible for the initial observations on the impact of CSFP and glaucoma re- ported a series of new observations at the Association for Research in Vision and Ophthalmology meeting in Fort Lauderdale in May. "We have conducted a study to evaluate whether age influences CSFP," he said. "If so, might changes in CSFP with age explain why ad- vancing age groups are more suscep- tible to developing glaucoma?" Age effects The group retrospectively reviewed the charts of nearly 34,000 patients who had previously undergone lum- bar puncture at the Mayo Clinic in Rochester, Minn. After excluding pa- tients with no opening pressure measurements or those who had rea- sons for abnormal opening pres- sures, nearly 14,000 remaining records were included for analysis. Their results continue to sup- port their initial hypothesis linking CSFP and glaucoma. "CSFP declines steadily with age," Dr. Fleischman said, "espe- cially after the late 40s." He went on to say, "Many U.S.- based population surveys of primary open-angle glaucoma and normal- tension glaucoma have identified a large increase in disease prevalence from age 50 and above. The age range in which mean CSFP declines is similar to that when the preva- lence of primary open-angle glau- coma rises. Advanced age is therefore associated with both CSFP and the development of primary open-angle glaucoma." Body mass index effects Body mass index (BMI) is a parame- ter that characterizes weight as a function of height and is calculated as weight (in kilograms) divided by the square of height (in meters). "Decreased BMI has been inde- pendently recognized as a possible risk factor for primary open-angle glaucoma, both in the Barbados Eye Study and in a recent study of health alliance surveys," said Dr. Berdahl. In the latter study, he said, an increased BMI in women was a protective factor for glaucoma. He and his team postulated that the increased risk of glaucoma asso- ciated with low BMI might be medi- ated by CSFP. "Multiple studies have evaluated the relationship between BMI and CSFP with conflicting re- sults," said Dr. Berdahl. To further investigate the rela- tionship between BMI and CSFP, the group reviewed 4,800 charts of pa- tients at the Mayo Clinic who un- derwent lumbar puncture and also had BMI documented in their records. As it turns out, CSFP increases as BMI increases. "At a healthy BMI of 18, the mean CSFP is about 113 mmH2O," said Dr. Berdahl. "At a BMI of 21, CSFP has increased in a statistically significant fashion to a mean of 124 mmH2O. At a BMI of 35, mean CSFP has reached 166 mmH20. Overall, there was a 32% increase in CSFP be- tween those whose BMI was 18 and those whose BMI was 35," he said. Clinical implications "Our findings suggest that as BMI increases, CSFP increases as well," said Dr. Berdahl. "Under the premise that low CSFP may be an independ- ent risk factor for developing glau- coma and elevated CSFP may be protective, this study indirectly sug- gests that an elevated BMI may pro- tect against glaucoma due to a corresponding increase in CSFP. Conversely, a lower BMI may in- crease the risk of the development of glaucoma. However, this remains a controversial issue." "These data provide additional evidence in support of the hypothe- sis that decreased CSFP may be a risk factor for primary open-angle glaucoma and offers a new explana- tion as to why the risk of glaucoma increases with age," said Dr. Fleischman. EW Editors' note: Drs. Berdahl and Fleischman have no financial interests related to this article. Contact information Berdahl: johnberdahl@gmail.com Fleischman: david8fleischman@gmail.com February 2011 December 2011 by Tony Realini, M.D., M.P.H. Is cerebrospinal fluid pressure a piece of the glaucoma puzzle?

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