The reference axis in corneal refractive surgeries: Visual axis or the line of sight?

Abstract

A reference axis for proper centration of the corneal working zone in refractive surgical techniques is required. This is difficult to define due to the fact that the human eye is not an aligned optical system. This theoretical note critically reviews and discusses the two commonly used reference axes; line of sight and the coaxially sighted corneal reflex. Taking into consideration the Stiles—Crawford effect, it is concluded that the coaxially sighted corneal reflex is remarkably close to the visual axis (or nodal axis) and is the preferred reference axis.