Factors affecting ocular rigidity in normal human eyes

Abstract Purpose To measure the ocular rigidity coefficient and evaluate its relation with axial length (AL), age and mean systemic blood pressure (SBP). Methods Sixty three patients (63 eyes) undergoing cataract surgery, with different refractive errors and no ocular or systemic pathology were enrolled in this study. An invasive, computer controlled device comprising a microdosimetric pump and a pressure sensor, is connected to the anterior chamber under topical anaesthesia with drops. The system is used to raise the intraocular pressure (IOP) from 15 to 40mmHg, by infusing the eye with a saline solution. After each 4 ul infusion step, the IOP is continuously recorded for 2 seconds. From an initial level of 40mmHg an IOP decay curve of 1 minute is obtained. SBP and pulse rate are measured during the procedure. The rigidity coefficient is calculated by an exponential fit to the pressure volume data after correction for outflow. The study was approved by the Institutional Board and performed under the patient’s informed consent. Results Mean AL was 24.8 (range 21.2‐32.5). Mean age and SBP was 59 (12) years and 93.7 (10.5) mmHg respectively. The mean ocular rigidity coefficient was 0.021 (0.005) ul‐1. Increasing axial length is associated with a decrease in the rigidity coefficient (r=‐0.61, p<0.01). A positive correlation between the rigidity coefficient and age of the patients is found (r=0.31, p=0.01), whereas similar findings were not observed for SBP (p>0.05). Conclusion This manonetric approach of measuring ocular rigidity provides a normative database of this parameter in living human eyes. Axial length and age influence ocular rigidity. These results may have implications on tonography and ocular pulse studies.