A model of inhomogeneous expansion of the cornea and stability of its focus.

A simple derivation of an analytical condition for expanding the cornea to get the stable position of the corneal focus is given. The corneal thickness increases from the apex till the limbus and the corneal shell expands inhomogeneously as a result of changes in intraocular pressure conditions. It expands more in the centre of the cornea and less at its apex. As a result the expansion changes the paraxial radius of the corneal curvature by the value of delta r as well as displaces the position of the centre of the central corneal curvature by the value of s. Presented paraxial calculations show that the position of the corneal focus is stable and insensitive on the expansion of the cornea if the ratio of both values amounts to about 0.34. Comparison of analytical results with published results of experiments on expanding intact cornea in vitro indicates their high accordance. This suggests a new, important role of the thickness distribution of the cornea.