The modelling of the influence of a corneal geometry on the pupil image of the human eye

In normal conditions, a pupil of the eye is observed through the optical system of the cornea. The cornea is the anterior surface of the eye and is the major refractive element of the human eye. The influence of the corneal shape should not be neglected in measurements of the pupil size. The purpose of this study was to estimate the influence of the corneal geometry, the diameter of the pupil and its position in the anterior chamber on the magnification and position of the image of the pupil. The numerical calculations presented in the paper assume infinitely thin cornea, and the corneal topography was approximated by the elongated ellipsoid. The ray tracing procedure was used in our numerical modelling. The magnification of the pupil image amounted to about 10% and increases with decrease of radius of curvature and eccentricity of the corneal profile and decreases for the largest pupil. The results show also that the pupil image is placed nearer the corneal apex than the real pupil. The image of the pupil is always blurred, which limits the sharp observation of the pupil.