Contribution of cornea to the peripheral ocular refraction in the two-dimensional visual field

Abstract

The evaluation of the contact lenses for myopia control is often focused on the change in corneal refractive power, which is applied to indicate the contribution of the cornea to the peripheral ocular refractions (POR). However, this concept lacks a direct relationship to the POR for a realistic human eye with structural and optical irregularities. In this study, we propose a mathematically rigorous and highly efficient procedure for specifying the contribution of the cornea to the POR based on the wavefronts propagating along the chief rays from the iris center to the entrance pupil center. Using generalized ray tracing, the complexity in the impacts of the geometry of both corneal surfaces and their orientation within the human eye are fully explained with analytical equations. As a case study, the proposed procedure is performed on a realistic corneal model constructed from the measurement data on children. An approximately linear relationship has been found between the POR and the vergence of the wavefronts at the iris center for all the visual field locations. Based on this finding, we find that the contribution of the cornea to the POR can be summarized by the slope and intercept parameters derived from the linear fits in the two-dimensional visual field. The proposed analysis procedure provides a powerful tool for evaluating the peripheral optical effects of the contact lens design.