Photo produced with color Doppler imaging, a noninvasive ultrasound technique that permits the measurement of blood flow velocity in vessels behind the eye. The left portion of the photo shows the image of a person's eye (black circular area) and the blood vessels supplying it from behind. The graph on the right represents the changing blood velocity in one of these vessels over several heartbeats. Alon Harris, Professor of Physiology, Biophysics, and Ophthalmology, School of Medicine, has used this technique to show that some persons with glaucoma have increased resistance to blood flow in the vessels behind their eyes and that this resistance may be reduced with certain treatments.