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The relation between type-2 diabetes (T2D) and glaucoma-related traits remains controversial. The authors analyzed structural and functional progression in primary open glaucoma (POAG) patients stratified by T2D status in the Diagnostic Innovations in Glaucoma Study cohort. In univariate analysis, the global retinal nerve fiber loss on Spectral Domain Ocular Coherence Tomography was 0.40 microns/year in the POAG/T2D+ group versus 0.83 microns/year in the POAG/T2D- group (p = 0.01). The difference in the temporal superior quadrant loss (0.33 microns/year vs 1.34 microns/year for the POAG/T2D+ and POAG/T2D- groups, respectively; p = 0.001) was more impressive and would survive conservative corrections for the multiple comparisons of all parameters that were assessed. The authors report that the differences in structural progression remained significant after correction for age, sex, race, mean IOP during follow-up, baseline mean deviation and hypertension. While a similar trend was found in the visual field parameters, the differences were not statistically significant. Mean follow-up in both groups was comparable: 6.2 years versus 5.6 years in the POAG/T2D+ and POAG/T2D- groups, respectively.
Almost every T2D patient had both eyes enrolled (55 eyes of 32 patients) compared to 142 eyes of 111 patients without T2D. T2D is a systemic disease that would affect both eyes of each patient. Thus, the results from the eyes in the T2D arm are highly correlated with one another and this could have a major impact on study outcome. The study would benefit from having only one eye from each arm enrolled.
71.9% of T2D patients were using metformin. Thus, the geroprotective effect of this drug1 and not T2D itself, could be mediating the results reported here
Notably, T2D was not associated with more rapid structural progression in this study. As the authors point out, 71.9% of T2D patients were using metformin. Thus, the geroprotective effect of this drug1 and not T2D itself, could be mediating the results reported here. More work is needed to explore the relation between T2D and glaucoma-related traits.