1. An apparatus for monitoring the position of an eye during a laser ablation treatment of the eye, the apparatus including: an imaging sub-system to record an instantaneous image of a first region of the eye of the patient, which first region traverses the limbus of the eye and to analyze said image to derive a first indication of the location of the limbus in said first region at first intervals; first optics configured to direct an incident beam along an optical path onto the external surface of the eye so as to illuminate a second region of said surface, which second region includes a segment of the limbus of the eye, and to receive a return beam comprising light of said incident beam scattered by said second region; and at least one detector configured to detect said return beam and to determine a second indication of the location of the limbus in said second region of said surface, at second intervals, wherein the second intervals are substantially shorter than the first intervals; the apparatus being configured to determine in response to said first indication the position of the eye at said first or greater intervals, and in response to said second indication update that position within said first or greater intervals.