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Editors Selection IGR 12-2

Glaucoma and systemic diseases: IOP and hyperglycemia

Comment by David Friedman & Lucie Mudie on:

67227 Increased Intraocular Pressure and Hyperglycemic Level in Diabetic Patients, Hymowitz MB; Chang D; Feinberg EB et al., PLoS ONE, 2016; 11: e0151833

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The relationship between hyperglycemia, diabetes mellitus (DM) and glaucoma has been subject to scrutiny in many population based studies, as well as systematic reviews and meta-analysis. Neither the Baltimore Eye Survey nor the Rotterdam Eye Survey found an association between DM and POAG, however a recent meta-analysis reported that those with diabetes have 1.5 times the risk of glaucoma as those who do not have diabetes.¹ Hymowitz et al. retrospectively reviewed 114 charts of patients with non-proliferative diabetic retinopathy who did not have glaucoma. The group had poorly-controlled diabetes with a mean HbA1c above 8%. Rather than analyze the data using continuous values, the authors compared those with IOP < 14.5 to those with IOP of 14.5 mmHg or higher, and found that HbA1c was higher in those with higher IOP (9.0% versus 8.1% respectively). Furthermore, none of those with HbA1c above 9.5% had IOP < 14.5 mmHg.

The authors found that HbA1c was higher in those with higher IOP

The relationship between HbA1c does not appear linear, however, and at HbA1c levels lower than 9.5% the association with IOP appears minimal at best. The authors only provide a cursory analysis of the data, and details about those excluded are not provided. Furthermore, it is unclear how IOP data were handled for both eyes; was an average IOP used or did each eye of a subject individually contribute to the results? It is also unclear whether any covariates were adjusted for in this analysis.

The authors support their results with their prior mouse study showing that hyperglycemia induces changes in the extra cellular matrix of the trabecular meshwork, potentially leading to decreased outflow of aqueous humor and increased IOP. Despite limitations, the author's finding that in this set of patients those with very high HbA1c almost never had a low IOP is intriguing and would be worth confirming.

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