Corneal biomechanical properties in primary open angle glaucoma and normal tension glaucoma

Purpose: To determine and compare the corneal biomechanical properties between eyes with primary open angle glaucoma (POAG) and eyes with normal tension glaucoma (NTG). Patients and Methods: Prospective cross-sectional study. Consecutive eligible POAG and NTG patients attending the Glaucoma Clinic had assessment of their corneal biomechanical properties-corneal hysteresis (CH) and corneal resistance factor (CRF)-using the Ocular Response Analyzer by an observer masked to the diagnosis. Exclusion criteria included previous intraocular surgery, corneal pathology, inflammatory connective tissue disease, and refraction of 5-dimensional or over. If both eyes were eligible, then the right eye was used for analysis. The main outcome measures were corneal hysteresis and CRF measurements. Data analysis was performed using the t test and general linear model. Results: Eighty-one patients (80 whites) were analyzed. Forty had NTG, whereas 41 had POAG. Thirty-five were females. There was a statistically significant difference in mean CH (NTG 9.6 +/- 1.3 min Hg; POAG 9.0 +/- 1.4 mm Hg; P = 0.01), but not in mean CRF (NTG 9.9 +/- 1.4; POAG 10.8 +/- 1.7; P = 0.06). The highest recorded Goldmann applanation intraocular pressure (IOP) was statistically significantly associated with lower CH (P = 0.01) and higher CRF (P = 0.02). Conclusions: There was a small but statistically significant difference in the mean CH between POAG and NTG (CH was higher in NTG). The highest recorded Goldmann applanation IOP was also statistically significantly correlated with lower CH and higher CRF, suggesting that alterations to the corneal biomechanical properties may occur as a result of chronic raised TOP in POAG.