Figure 5.

The ray tracing method for estimating the pupil center. Pc is the pupil center, Cc is the cornea center, û_i is a point in the pupil perimeter, u_i is a point in the corneal surface, K_i is a unit vector between these, k_i is the image point of u¡ , k¡ is the unit vector between these, and O denotes the optical center. The ray k¡ refracts at the cornealsurface because the refractive index of the cornea is nc > 1. The figure is adapted from Hennessey et al. (10).