1. A method for performing eye registration for a patient's eye, comprising: obtaining a first eye image by a first diagnostic device and defining a reference coordinate system; obtaining a second eye image by a surgery device, said second eye image being obtained in a pre-surgery phase before the surgery has started; performing a first registration between the first eye image and the second eye image to obtain a first registration result; obtaining a third eye image by the surgery device, the third eye image being obtained after surgery has started; performing a second registration between the second eye image and the third eye image to obtain a second registration result; and combining the first and second registration results to obtain a combined registration result to thereby obtain a registration between the first eye image obtained by the diagnostic device and the third eye image obtained by the surgery device after surgery has started; wherein the first eye image taken by the diagnostic device and said third eye image taken by the surgery device are taken under significantly different eye conditions that can negatively affect a direct registration between the first eye image and the third image, the different eye conditions comprising the eye having no suction ring being placed on it when the first image is taken and the eye having a suction ring being placed on it when the third image is taken.