1. In an ocular diagnostic device for obtaining a diagnostic measurement of a patient's eye indicative of a wavefront aberration of the eye, and an iris image of the patient's eye associated with the diagnostic measurement, including an iris image capture component, a diagnostic measurement component and a visible illumination fixation source, the improvement characterized by, the fixation source having a controllable visible illumination level suitable for causing a controllable change in the size of the pupil of the patient's eye.