EyeWorld India March 2013 Issue

49 EWAP GLAUCOMA March 2013 Studies highlight the relationship between diet and glaucoma C an what we eat increase our risk of getting glaucoma? A trio of studies presented at this year’s American Glaucoma Society meeting suggested that the answer might be yes. The pathophysiology of glaucoma is poorly understood. The primary risk factor, IOP, has a complex relationship with the disease, being frequently elevated but neither necessary nor sufficient to explain the majority of cases of glaucoma. Based on the high risk of glaucoma among first-degree relatives, a genetic basis is strongly suspected. Major genetic studies, however, have failed to find a gene or genes that account for more than a small percentage of primary open- angle glaucoma cases. This has led many to speculate that gene- environment interactions may be at play. This is a two-hit mechanism of sorts: having the gene isn’t enough—one must also have a specific environmental exposure. To date, the nature of such an environmental factor has been unknown. New data suggests that it might be diet-related. Nutrients and oxidative stress “Oxidative stress may be an important component of the pathophysiology of glaucoma,” said Sophia Wang, BA , medical student, University of California- San Francisco, Calif., USA. Calcium and iron, she said, are two dietary elements that play a role in the formation of highly reactive oxygen species that can damage tissues. She proposed that high dietary intake of these nutrients, coupled with impaired regulation of homeostatic regulatory processes due to aging, could lead to damage to the trabecular meshwork, loss of retinal ganglion cells, and the clinical manifestations of glaucoma. To explore this hypothesis, Ms. Wang conducted a cross-sectional epidemiologic study utilizing the National Health and Nutrition Examination Surveys (NHANES) database, which contains detailed information on the dietary intake of large numbers of Americans as well as their glaucoma status by self-report. “We analyzed data from 3,833 adult Americans, of whom 248 self-reported having glaucoma,” she said. Ms. Wang found that people consuming the highest levels of calcium—more than 800 mg/ day—were 2.4 times more likely to self-report having glaucoma than those consuming the lowest levels of calcium. Also, people consuming the highest levels of iron—more than 18 mg/day—were 3.8 times more likely to self-report glaucoma than those consuming the lowest levels of iron. People consuming the highest levels of both calcium and iron, she said, had a 7.2 fold higher odds of glaucoma. Louis Pasquale, MD, Massachusetts Eye and Ear Infirmary, Boston, Mass., USA, said, “This is the first human data in support of an oxidative stress mechanism in glaucoma.” Can diet influence the risk of glaucoma? by Tony Realini, MD Caffeine Dr. Pasquale has studied the incidence of pseudoexfoliation glaucoma between 1980 and 2008 and its relationship to caffeine intake utilizing the Nurses Health Study database. This database included data on nutritional intake as well as findings on eye examinations. He identified 300 new cases of pseudoexfoliation glaucoma among 1.6 million person-years of follow-up. “We observed a positive association between overall caffeine intake and pseudoexfoliation that was not quite statistically significant,” he said. But for those who get their caffeine specifically from coffee—drinking at least three cups a day—the risk of pseudoexfoliation was 63% higher than for non-coffee drinkers. Interestingly, the effect of caffeine intake was modified by family history. “Among those consuming the highest levels of caffeine, people who also had a family history of glaucoma had a 2.9-fold higher risk of glaucoma, compared to only a 1.2-fold increase for those without a family history,” he said. This supports the concept of a gene-environment interaction for caffeine and pseudoexfoliation glaucoma, he said. Caffeine and IOP To evaluate how caffeine might affect glaucoma, Aliya Jiwani, in collaboration with Dr. Pasquale and others, conducted a randomized trial to explore caffeine’s effect on IOP and ocular perfusion pressure (OPP) in healthy subjects, glaucoma suspects, and patients with both low-tension and high-tension glaucoma. In their crossover study, patients drank an 8-oz. cup of caffeinated coffee at one visit and an 8-oz. cup of decaffeinated coffee at a second visit, in a randomized order. IOP and OPP were determined before and 60 and 90 minutes after each beverage. Compared to decaffeinated coffee, caffeinated coffee raised IOP by 1 mmHg at both time points, and raised OPP by 1.6 mmHg and 1.3 mmHg at 60 and 90 minutes, respectively. Although the changes were statistically significant, she said, the effect size was quite small. “Consuming a single 8-oz. cup of caffeinated coffee likely does not clinically impact IOP or OPP,” she concluded. Dr. Pasquale agreed. “This is the beginning of a conversation about the role of environmental factors associated with the development of glaucoma,” he said. “It is still too early to begin recommending lifestyle changes for our glaucoma patients.” But he sees the potential for significant progress in this research area in the future. “We may be able to prevent pseudoexfoliation glaucoma in the decades to come,” Dr. Pasquale said. EWAP Editors’ note: Ms. Wang has no financial interests related to this article. Contact information Jiwani: aliyajiwani@gmail.com Pasquale: louis.pasquale@meei.harvard.edu Wang: wang@ucsf.edu