On the dependence of outflow facility on Intraocular pressure in the living human eye.

Abstract

Abstract Purpose The change of outflow facility is determined by the value of intraocular pressure (IOP) possibly due to changes in the angle of the anterior chamber, the trabecular meshwork and the Schlemm’s canal. The purpose of this study was to determine the relationship between outflow facility and IOP (especially for elevated values of IOPs) in living human eyes. Methods Thirteen eyes from thirteen cataract patients (6 men and 7 women, aged 61 years, sd 15) were enrolled in the study. The study was approved by the Institutional Review Board. The measurements were performed before cataract surgery, using an intraoperative invasive manometric device. The pressure‐time decay was recorded in order to calculate the outflow facility at different values of IOP. An appropriate mathematical model was developed to calculate outflow facility based on the IOP‐time curve and the ocular rigidity of each eye under measurement. Results The average outflow facility coefficient was 0.213 (SD 0.097) μl/min/mmHg. Our data suggest that outflow facility has a non‐linear relationship with IOP, especially in the range of higher IOPs. This non‐linear behavior of outflow facility was approximated with an exponential function. There was no significant statistical correlation (r=0.2377, p=0.4568) with outflow facility and ocular rigidity. Conclusion Outflow facility depends on IOP in a non‐linear manner that indicates a complex relationship between IOP and the geometry of the outflow pathways. In this limited set of measurements, a relationship between the outflow facility (or its non‐linearity) with other parameters could not be established.