JUL 30, 2008
Theoretical models and animal studies have suggested that glaucomatous damage may be related to altered biomechanical properties of the sclera and optic nerve head. The current article reports on an interesting study conducted with human subjects that confirms the results of ex vivo and animal studies that suggest that altered biomechanical properties, in this case stiffness, of the globe particularly at the lamina cribrosa in primary open-angle glaucoma (POAG) patients play a role in axonal damage.
The study's authors measured ocular rigidity or stiffness in 70 POAG patients and 70 healthy control subjects matched for age, gender, IOP and systemic blood pressure. Ocular rigidity calculations were based on a modified version of the Friedenwald equation that computes rigidity based on logarithmic differences in IOP and ocular volume change. The researchers used in their calculations pulse-related IOP changes that were measured by pneumotonometry and computed the change in volume by measuring fundus pulsation amplitude with laser interferometry.
The study's results suggest that ocular rigidity or structural stiffness as calculated by this method is significantly higher in patients with POAG than in healthy controls. The stiffness factor measured showed a relationship with both mean arterial pressure and diastolic blood pressure. Additionally, in POAG and control subjects the stiffness factor positively correlated with ocular perfusion pressure but was independent of age, sex, systolic blood pressure, pulse pressure amplitude and pulse rate.
The authors discussed some of the study's limitations, which include the fact that they did not determine if their results were reproducible and the possible influence on ocular rigidity of topical medications used by the subjects with POAG.
Dr. Edward is a consultant to Alcon Laboratories, Inc., and Allergan, Inc. He receives lecture fees from Alcon Laboratories and Allergan and grant support from Alcon Laboratories and Pfizer Ophthalmics.