The previously described maps show curvature changes. Another way to show the corneal data is by ray tracing refractive power maps. With ray tracing using Snell's Law the actual power change across the anterior surface of the cornea can be determined. This gives a different picture in that the power increases towards the periphery due to the increasing angle of incidence the rays make to the cornea in the periphery. This power change represents the spherical aberration of the cornea.
