a real - time refractory control system includes a laser refractive surgery instrument for modifying the refraction of the eye , an objective diagnostic apparatus for measuring the refraction and aberrations of the eye , and an aperture - sharing element to inject a refractive surgery beam and a monitoring diagnostic beam . an associated method of adjusting a refraction of an eye , includes : performing a procedure to modify the refraction of the eye ; while the procedure is being performed , measuring the refraction and / or an aberration of the eye ; and terminating the procedure when a change in the measured refraction and / or the measured aberration reaches a desired value .