Validity of the Imbert-Fick law for constant-pressure tonography

In the clinical evaluation of constant-pressure tonography, charts are required by the medical technician for determining the value of aqueous outflow facility from the force readings obtained from the tonography instrument. The accuracy of the tables depends upon the validity of Imbert-Fick law in this application. As a result of earlier experiments on excised human corneas, there has been some question as to whether use of this law leads to large errors when applied to corneal applanation, and it has been suggested that use of an empirical relation would be better. In this study the accuracy of the Imbert-Fick law was tested with the use of rabbit and human cornea, and in the intact and the enucleated rabbit eye. Our results also do not conform exactly to the Imbert-Fick law, but the errors are not excessive for the practical application of the law to constant-pressure tonography. In fact, its use leads to errors of lesser magnitude than errors from other sources in the constant-pressure measurement of aqueous outflow facility.