EyeWorld Asia-Pacific December 2012 Issue

44 EWAP GLAUCOMA December 2012 IOP and glaucoma: What really matters? by Tony Realini, MD Discussing the issues that do and do not matter in lowering IOP T he relationship between glaucoma and IOP is complex. Once a required characteristic of the disease, elevated IOP is no longer considered to be a part of the definition of glaucoma. IOP has been demoted to risk factor status, but an extremely important risk factor: It is the only modifiable risk factor, and lowering IOP is the only established treatment for glaucoma. Given its critical importance in disease management, an international group of experts at the World Ophthalmology Congress in Abu Dhabi met to discuss the issues that do and do not matter when lowering IOP. Which matters more: peak IOP or mean IOP? “IOP varies throughout the day and the night,” said Remo Susanna, Jr., MD, University of Sao Paolo, Brazil. “In terms of glaucoma progression, which is the more important parameter: mean IOP or peak IOP?” The question is difficult to answer in large part because the acquisition of diurnal and nocturnal IOP data is expensive, time-consuming, and inconvenient for both the patient and the doctor. “Twenty-four hour circadian IOP curves are ideal but impractical,” he said. “The costs and labor involved make this difficult or impossible in daily practice. And continuous IOP monitoring is the ‘holy grail,’ but it isn’t ready for clinical use at this time.” This leaves two choices. “We can get a diurnal curve from 8 a.m. to 6 p.m. on a single day, checking IOP every 2-3 hours. Or we can see patients at different times of the day at each visit and construct a diurnal curve over time,” Dr. Susanna said. The issue is further complicated by the recent observation that IOP variation is inconsistent from day to day. “Reproducibility of IOP fluctuation is poor,” he said. So establishing a diurnal IOP curve on a single day may be less informative than physicians have previously believed of IOP on other days. Several post-hoc analyses of major clinical trials have suggested that IOP may be an important predictor of future progression, but these results have been mixed. A more recent analysis from de Moraes and colleagues at New York Eye and Ear Infirmary, published in the Archives of Ophthalmology, suggested that peak IOP was more predictive of future glaucoma progression than mean IOP. Gardiner1 also found that maximum IOP may be a more important risk factor than mean IOP over the same time period. These findings were in agreement with Dr. Susanna’s research involving the water drinking test, a stress test to estimate peak IOP by measuring the IOP spike that occurs after consuming 800 mL of water in 5 minutes time. The IOP is measured after 15, 30, and 45 minutes of consuming the water. The maximum IOP of these three IOP measurements is considered the peak of the water drinking test. “There is strong correlation between the peak IOP after the water drinking test and glaucomatous visual field progression,” he said. He concluded that “there is suggestive evidence that peak IOP is important, but fluctuation seems less important as a risk factor for glaucoma progression.” Target IOP: Is it important? “IOP is the main risk factor for glaucoma and its progression and the only risk factor that we have treatment for,” said Esther Hoffmann, MD, University of Mainz, Germany. “But there is no clearly defined single IOP level below which an individual eye with glaucoma is completely safe from progression.” The goal of glaucoma therapy, she said, is to preserve quality of life in glaucoma patients. “However, we do not know the stage of glaucoma, the IOP level, or the age at which quality of life starts to deteriorate in a significant way.” Thus, the determination of target IOP must be customized for each patient, and perhaps for each eye, based on the individual patient’s risk profile. “Three primary considerations factor into the target IOP determination,” Dr. Hoffmann said. “These are the stage of glaucoma, the life expectancy of the patient, and the IOP level at which prior damage occurred.” As for coming up with the exact target IOP value, she said that this is as much art as science. “Target pressure should be a range rather than an absolute number. It is not an absolute. It is a best guess, a useful and practical way to simplify our lives in the clinic by defining our therapeutic goals.” She added, “Once set, the target IOP should not be considered set in