On the role of biconic surfaces in modelling astigmatic eyes

This study provides a detailed description of biconic surfaces, focusing on their critical properties and utility in modelling astigmatic eyes. It examines general aspects, including implicit or explicit equations, azimuthal variations as well as average values of their geometrical parameters, and matrix-vector formulation. Additionally, the study explores the properties of these surfaces under conditions where the principal curvatures are closely matched, reflecting the typical characteristics of astigmatic eyes. The derived expressions closely align with theoretical predictions, and these conditions are successfully tested on 56 healthy corneas. This work expands current knowledge about biconic surfaces and offers a deeper understanding of the optical features of astigmatic eyes.