Eyeworld

Reporting from the 6th World Glaucoma Congress, June 6–9, 2015, Hong Kong EW MEETING REPORTER 70 very small sample of data. Consider the near impossibility of managing diabetes on the basis of 3 random blood glucose levels annually. A few random IOP measure- ments per year—limited to office hours—poorly characterizes the complexity of IOP as a dynamic biological parameter. IOP varies throughout the day, and from day to day, and the factors that drive this variability are poorly understood. "Anything that you can do while you are alive can affect your IOP," said Arthur Sit, MD, Rochester, Minn. Peak IOP—which many be- lieve is a fundamentally important aspect of IOP control in glaucoma patients—usually occurs at night in most patients. Continuous IOP monitoring is on the near horizon. Until then, we have several tools and techniques available to more comprehensively characterize IOP. These include a single-day diurnal IOP curve, a so-called poor man's diurnal curve comprised of IOP measurements at different times of day on different days, and various provocative tests such as supine IOP measurement and the water-drink- ing test. When utilized correctly, said Remo Susannah, MD, São Pau- lo, Brazil, these approaches can give us a more comprehensive picture of IOP behavior than a handful of random sitting IOP measurements. Not every one of our glauco- ma patients warrants these efforts, said Carlos Gustavo de Moraes, MD, New York. The patient with well-controlled IOP and stable visual fields has no need for further exploration of IOP behavior. In contrast, the patient whose glauco- ma is progressing despite apparently well-controlled IOP may be a good candidate for a more comprehensive IOP assessment. Supine IOP or a wa- ter-drinking test—in which the pa- tient consumes 1 liter of water over 5 minutes and IOP is checked every 15 minutes for the next hour—may reveal IOP peaks comparable to those that occur when patients are lying in bed asleep at night. EW Editors' note: The physicians have no financial interests related to their comments. optic neuropathy. In clinical studies, patients with glaucoma tend to have lower ICP than healthy subjects, and patients with normal-tension glaucoma have lower ICP than those with high-tension glaucoma. These observations suggest that the value of IOP relative to ICP—the translam- inar pressure difference of IOP and ICP—may be important. Because the lamina cribrosa separates the intra- ocular and intracranial spaces, its structure is also important. A thick lamina may better protect axons from high translaminar pressure differences; conversely, the lamina becomes thin in glaucomatous eyes and may offer less protection to the axons. "The translaminar pressure gradient is defined as the translam- inar pressure difference divided by laminar thickness, and may be an important biomarker for glaucoma risk," said Dexter Leung, MD, Hong Kong. A significant limiting factor in research related to ICP and glauco- ma is that ICP cannot currently be measured noninvasively. A new de- vice is ready for commercialization in Europe and is under review by the FDA in the United States, said Eun Ji Lee, MD, Seoul. It works similarly to a blood pressure cuff, which non- invasively measures intra-arterial pressure: external pressure is applied to the eye until flow in the intra- ocular and extraocular segments of the ophthalmic artery are equalized by Doppler imaging. The external pressure necessary to equalize flow approximates ICP. Editors' note: The physicians have no financial interests related to their comments. Comprehensive IOP assessment While IOP is not a significant com- ponent of the diagnostic process in glaucoma, it remains a fundamental- ly important means of assessing the effectiveness of therapy. Because IOP cannot currently be easily measured at home by patients or family mem- bers—in contrast with blood pres- sure and blood glucose—physicians are compelled to make important management decisions based on a Examining the optic nerve head The optic nerve head examination remains the most important aspect of both diagnosis and management of glaucoma. Remo Susannah, MD, São Paulo, Brazil, reviewed a systematic method for evaluating the optic nerve. First, focus on the rim, not the cup. Pay attention to the parapapillary region for signs of beta-zone atrophy, particularly in non-temporal sectors. Look for nerve fiber layer defects. Assess the lamina cribrosa for acquired optic nerve pits. And remain vigilant for disc hemorrhages, which are easily overlooked. There are a number of errors we commonly make in assessing the optic nerve head, said Michael Coote, MD, Melbourne, Australia. He is associated with the Glaucoma- tous Optic Neuropathy Evaluation program, a web-based system that has let more than 6,000 profession- als hone their skills at clinical optic nerve assessment. "The risk of glaucoma is overes- timated in large optic nerves, as the large physiologic cup can fool us," he said. Likewise, we often underes- timate risk in small optic nerves, where a modest cup may appear healthy but is actually atypical of small nerves, which typically have a small cup and a crowded appear- ance. Peripapillary atrophy also leads to underestimation of risk, as the atrophic region can be mistaken for rim, making the nerve appear healthier than it is. Editors' note: The physicians have no financial interests related to their comments. Glaucoma as a two- pressure disease IOP has long been linked with glaucoma, but as a risk factor, IOP is neither necessary nor sufficient to explain all cases of glaucoma. Further, the mechanism by which IOP leads to glaucoma damage has remained controversial. New thinking about the patho- genesis of glaucoma implicates intracranial pressure (ICP) as a significant factor in glaucomatous July 2015

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