A surgical system for an eye, the system comprising: a laser having an output surface, the output surface comprising a first sensing element； and a patient interface having a first end and a second end, the first end of the patient interface configured to couple to the laser, the second end configured to couple to the eye, the patient interface comprising: an interface lens having a first surface and a second surface, the first surface of the interface lens configured to contact the eye； and a second sensing element coupled to the second surface of the interface lens, the laser operable to couple the output surface with the second surface of the interface lens； the system further comprising a detector coupled to the plurality of capacitive electrodes, the detector configured to: determine when at least one of the plurality of capacitive electrodes couples to the second surface of the interface lens； and determine a capacitance change between the plurality of capacitive electrodes, the capacitance change indicating a relative position of the output surface of the laser with the second surface of the interface lens, wherein the first sensing element comprises a plurality of capacitive electrodes, wherein the second sensing element comprises a dielectric.
