A system of defining a reference axis of a patients eye in an external coordinate system, comprising: a light source for directing a light beam on a reflective surface associated with the patients eye, an imaging system for recording an image of a limbus of the patients eye and an image formed by a reflection of the light beam from a cornea of the patients eye, and a processor operatively connected to the imaging system to, from the image of the limbus, determine the center of the limbus of the patients eye in the external-coordinate system, and, from the image of the reflection, determine when the position of the reflection is coincident with the center of the limbus, at which position an axis normal to the cornea defines the reference axis.
