Abstract: An apparatus and method for actively compensating for pupil centroid shift includes obtaining a first measurement of a first reference point relative to a predetermined reference frame, wherein the first reference point being associated with a first pupil diameter of a patient. The method further includes obtaining a second measurement of a second reference point relative to the predetermined reference frame, wherein the second reference point is associated with a second pupil diameter of the patient and the second pupil diameter is different from the first pupil diameter. The method still further includes actively determining a relationship between the first measurement and the second measurement and actively generating a correction in response to the relationship, wherein the correction being used by a treatment laser in association with an eye surgery.