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Meta-analysis finds diabetes linked to increased risk for glaucoma
Results support the recommendation that patients with diabetes be referred to ophthalmologists for glaucoma evaluation.
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Diabetes, duration of diabetes and fasting glucose levels are all associated with a significantly increased risk for glaucoma, according to a meta-analysis.
Diabetes and fasting glucose levels were also linked to slightly higher IOP, according to the retrospective analysis of nearly 3 million individuals from 16 countries included in 47 studies.
“The association between diabetes and glaucoma is an extremely important and controversial topic,” lead author Di Zhao, PhD, said. “When searching the literature for our own studies of diabetes and metabolic risk factors with glaucoma risk, we came across studies with different conclusions on the direction and strength of the association. We thought that a systematic review and meta-analysis for examining this association would be very helpful for synthesizing the available evidence and for providing a state-of-the-science reference for ophthalmologists and clinical investigators.”
Di Zhao
Findings
Patients with diabetes had a 48% increased risk for glaucoma compared with those without diabetes. The average risk for glaucoma increased by 5% for each year of increase in diabetes duration.
“However, there was very limited evidence on the association between metabolic syndrome or blood glucose levels and glaucoma,” Zhao told Ocular Surgery News.
A study from Malaysia suggested that metabolic syndrome has a protective effect against glaucoma, whereas another study among Latinos in the U.S. showed that high blood glucose level lacks a significant association with the risk for glaucoma.
“This evidence, though, is insufficient to establish a firm conclusion,” Zhao said.
Because glaucoma is a major cause of blindness, and because the metabolic syndrome and associated metabolic abnormalities are common, Zhao said that this topic of research may have an important impact on clinical practice and public health.
In the meta-analysis, on average, IOP was 0.18 mm Hg higher in patients with diabetes than in those without. In addition, each 10 mg/dL increase in blood glucose level was associated with an average increase in IOP of 0.09 mm Hg.
The risk for ocular hypertension was 52% higher in patients with diabetes than in those without. The only study that linked fasting glucose levels to the risk for ocular hypertension was conducted in Japan.
“That study found that people with impaired fasting glucose had significantly increased risk for developing ocular hypertension,” Zhao said.
Although the authors were not surprised to find an association between diabetes and the risk for glaucoma, they were somewhat surprised by the degree of heterogeneity of the associations and the variability between studies, Zhao said.
“However, we were reassured that even among longitudinal studies, which are less prone to bias, there were positive associations,” she said.
Diagnostic bias
Because patients with glaucoma are more likely to be in contact with eye care providers, diagnostic bias is still a concern that requires additional research, according to Zhao.
“We were also very surprised by the scarcity of studies on prediabetes, metabolic syndrome and its components on the risk of glaucoma,” Zhao said.
The results of the meta-analysis support the recommendation that patients with diabetes be referred to ophthalmologists to evaluate glaucoma. In addition to education about diabetic retinopathy, patients with diabetes should also be educated about glaucoma, Zhao said.
“The clinical impact of the coexistence of diabetic retinopathy and glaucoma in these patients is a very important clinical issue,” she said.
Additional longitudinal studies on the associations are needed, according to the authors.
“Eventually, we may need to develop specific guidelines for glaucoma screening and management in patients with diabetes,” Zhao said.
The authors conducted a second study, now under review, assessing the cross-sectional associations between diabetes, glucose metabolism and the risk for glaucoma in the National Health and Nutrition Examination Survey.
“We found that diabetes, prediabetes and prolonged diabetes duration were associated with higher prevalence of glaucoma,” Zhao said. “We also found that the prevalence of glaucoma was higher among people with increasing levels of biomarkers of glucose metabolisms, including blood glucose, hemoglobin A1C and insulin resistance.” – by Bob Kronemyer
References:
Chopra V, et al. Ophthalmology. 2008;doi:10.1016/j.ophtha.2007.04.049.Imai K, et al. Int J Obes (Lond). 2010;doi:10.1038/ijo.2010.32.
Tan GS, et al. Arch Ophthalmol. 2009;doi:10.1001/archophthalmol.2009.268.
Zhao D, et al. Ophthalmology. 2014;doi:10.1016/j.ophtha.2014.07.051.
For more information:
Di Zhao, PhD, can be reached at 2024 East Monument St., 2-607c, Baltimore, MD 21205; 410-614-0574; email: dizhao@jhu.edu.Disclosure: Zhao has no relevant financial disclosures.