Investigation of the liquid in‐ and outflow parameters of the human eye using a modified strategy of the mechanical loading test

Abstract

AbstractPurpose To obtain an additional information about the status of the inflow and outflow systems of the eye from ophthalmologic procedures based on static loading, with further application to diagnostics.Methods The standard method, based on static load application, for the estimation of parameters characterizing the aqueous humor dynamics was supplemented with an unloading test. After a four‐minute stationary mechanical loading by a Schiøtz tonometer, the load was removed and IOP was measured in a discrete regime for up to 20 min using the same tonometer. Clinical measurements were carried out on glaucoma (13) and non‐glaucoma (4) patients. The data obtained were processed using our mathematical model that represents the eyeball as an elastic water‐filled shell whose inner volume is regulated by dynamic balance between the liquid inflow and outflow and is assumed to be a function of IOP and the elastic and geometric characteristics of the system.Results The most important result is a strong difference between two characteristic times: the time that characterizes the rate of pressure fall under load and the time that characterizes the rate of pressure recovery after removing the load. The characteristic time is directly related with the outflow facility. The difference varies in different groups of patients. The results can be understood within the assumption of nonlinear IOP dependence of the outflow facility coefficient.Conclusion The modified mechanical loading test is a useful tool for investigating the biomechanical behavior of glaucoma and non‐glaucoma eyes. Our preliminary results give grounds to expect that the effect revealed may be applied to diagnostics.