An apparatus to treat a patient comprises a laser beam, a measurement module, a scanner and a curved patient interface lens. The curved patient interface is measured with a pattern so as to determine a plurality of distances of the curved surface at a plurality of measurement locations. The measurement pattern may comprise the plurality of measurement locations distributed about a central measurement axis corresponding to the laser treatment axis. The plurality of measurement locations of the curved surface may correspond to a portion of a planned treatment profile, such that the measured distances correspond to alignment of the planned treatment. The plurality of distances can be used to determine an apex of the curved surface of the patient interface and to align the laser treatment axis with the apex of the curved surface.