Comparison of optic nerve head topographic parameters in patients with primary open-angle glaucoma with and without diabetes mellitus

Purpose: To evaluate the optic nerve head (ONH) parameters of primary open-angle glaucoma (POAG) patients with and without diabetes and to investigate the effect of the metabolic control of diabetes on ONH topography. Materials and Methods: A study group of 60 eyes of 60 POAG patients with type 2 diabetes mellitus and a control group of 41 eyes of 41 POAG patients without diabetes were recruited for the study. Complete ophthalmic examinations of all patients were performed and the quantitative optic disc parameters were evaluated with Heidelberg retina tomography (HRT) III. HbA1c measurements of diabetic patients were assessed on the same day when the ophthalmic assessments were performed. Results: Mean rim area and rim volume of the study group was statistically higher than the control group (P=0.04 for rim area and P=0.02 for rim volume). The difference in other parameters of the HRT between the groups were insignificant (P>0.05). In the study group, the duration of the diabetes was not significantly correlated to rim area and rim volume (r=0.03, P=0.81 for rim area; r=0.03, P=0.79 for rim volume). Analysis of covariance showed insignificant effects of age, sex, MD, and PSD values over rim area and rim volume (P>0.05). There were weak but statistically significant correlations between HbA1c levels and some HRT parameters including disc area, cup area, cup volume, and cup shape measure (r=0.35 and P=0.006 for disc area; r=0.35 and P=0.006 for cup area; r=0.32 and P=0.01 for cup volume; r=0.32 and P=0.01 for cup shape measure). Conclusions: The results of this study imply the protective effect of diabetes over glaucomatous optic nerve damage in POAG patients. However, larger and controlled studies are warranted to confirm those findings.