1. A method of monitoring the position of an eye during a laser ablation treatment of the eye, the method including: directing an incident light beam along an optical path onto the external surface of the eye so as to illuminate a region of said surface that includes a segment of the limbus of the eye; detecting, with at least one detector having one or more detector segments, a return beam comprising light of said incident beam scattered by said surface region, which return beam returns back along said optical path and is separated from the incident beam at beam separation means, said detector segment(s) recording first and second values for light scattered respectively by the sclera and iris in said illuminated region; whereby movement of said limbal segment, and therefore of the eye, produces a change in at least one of said values.