Estimation of ocular rigidity based on pneumotonometric measurement of pulse amplitude and laser interferometric measurement of fundus pulse in patients with primary open angle glaucoma

¹ Clinical Pharmacology, Medical University of Vienna, Vienna, Austria
² Ophthalmology, Medical University of Vienna, Vienna, Austria
³ Clinical Pharmacology, Medizinische Universitat Wien, Waehringer Guertel 18-20, Vienna, Asutria, Austria

^* To whom correspondence should be addressed. E-mail: leopold.schmetterer{at}meduniwien.ac.at.

	Abstract

Purpose: There is evidence from theoretical models and animal studies that the biomechanical properties of the optic nerve head and the sclera may play a role in the pathophysiology of glaucoma. There are, however, only few data available which demonstrate such biomechanical alterations in vivo. We tested the hypothesis that patients with primary open angle glaucoma have an abnormal structural stiffness based on measurements of intraocular pressure amplitude and ocular fundus pulsation amplitude. Methods: Seventy patients with primary open angle glaucoma (POAG) and 70 healthy control subjects matched for age, gender, intraocular pressure and systemic blood pressure were included in this trial. The ocular pulse amplitude (PA) and pulsatile ocular blood flow were assessed with pneumotonometry. The fundus pulsation amplitude (FPA) was measured using laser interferometry. Based on the Friedenwald equation a coefficient of ocular rigidity (E1) was calculated relating PA to FPA. Results: There was no difference in systemic blood pressure, intraocular pressure, and ocular perfusion pressure between glaucoma patients and healthy control subjects. Both, FPA and PA were lower in patients with glaucoma than in healthy controls. The calculated factor E1 was significantly higher in patients with POAG (0.0454 ± 0.0085 a.u.) than in healthy control subjects (0.0427 ± 0.0058 a.u., p = 0.03). Multiple regression analysis revealed that E1 was independent of age and gender, and only slightly correlated with ocular perfusion pressure. Conclusions: The present study indicates increased ocular rigidity in patients with POAG. This is compatible with a number of previous animal experiments and supports the concepts that the biomechanical properties of ocular tissues play a role in the diseases process.

Key Words: glaucoma, blood flow, optic nerve head, biomechanics

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