Measurement of viscoelastic corneal parameters (corneal hysteresis) in patients with primary open angle glaucoma

Background. The ocular response analyzer (ORA) uses an air-pressure-triggered, dynamic, bi-directional corneal applanation method to measure biomechanical parameters of the cornea. Corneal hysteresis (CH) is defined as the difference in intraocular pressure recorded during inward and outward applanation. CH is therefore an indicator for the viscoelastic properties of the cornea. Patients and methods. CH was recorded in non-glaucoma patients (80 eyes) as well as in patients with primary open angle glaucoma (POAG, 82 eyes). The correlation between CH and central corneal thickness (CCT) was analyzed. Results. Mean CH was 10.6 +/- 2.2 mmHg in the non-glaucoma group and 9.3 +/- 2.2 mmHg in patients with POAG (p<0.01). CH and CCT showed a positive correlation in non-POAG patients, however no such correlation was found in the POAG group. Conclusion. Patients with POAG show an alteration of biomechanical corneal parameters with a significant decrease in corneal hysteresis. A positive correlation between CH and CCT, which was seen in the non-glaucoma group could not be detected in the POAG group.