Comparison of Optic Nerve Head Compliance and Corneal Biomechanics Between Diabetic and Non-diabetic Glaucomatous Patients

Abstract

Purpose: : To investigate changes in optic nerve head (ONH) topography after acute intraocular pressure (IOP) reduction and correlate these with corneal hysteresis in diabetic and non-diabetic primary open-angle glaucoma (POAG) patients.

Methods: : We enrolled 42 POAG patients (19 [34 eyes] with diabetes mellitus and 23 [36 eyes] age matched controls), with no other ocular disease or previous ocular surgery. Data collected by masked investigators included ultrasonic pachymetry and corneal hysteresis (CH) using the Ocular Response Analyzer. Heidelberg Retina Tomography III and Goldmann tonometry were performed before and 1 hour after pharmacological IOP reduction (topical timolol maleate 0.5% + brimonidine tartrate 0.2%, topical bimatoprost 0.03%, and oral acetazolamide 500 mg). The mean of 3 measurements was considered. Differences between changes in ONH topographic parameters in each group and their correlation with CH were calculated.

Results: : Mean ±SD CCT in diabetic and control groups were 532.9 ±31 and 550.6 ±36.2 µm respectively (p=0.178). Mean IOP reduction was similar in both diabetic (44.8%) and control (48%) groups (p=0.450). General linear model (correcting for interocular dependency) revealed greater ONH topographic changes (towards cupping reversal) in cup and rim area, and cup and rim volume in the control group comparing to the diabetic group (p<0.023). CH values were higher in the diabetic group (8.9 mmHg vs 7.8 mmHg in the control group) (p=0.048). Partial correlation coefficient showed that higher CH values correlated with a lesser degree of ONH topographic changes (p= 0.022, r=-0.297). Age, CCT, amount of IOP reduction and baseline IOP were not significant in this model.

Conclusions: : Topographic ONH changes are significantly lower in POAG patients with diabetes after acute IOP reduction compared to non-diabetic POAG patients. This could be a surrogate measure of lamina cribrosa compliance and/or other optic nerve head characteristics, which may imply in increased tissue rigidity in the ONH.

Keywords: optic disc