High-resolution ultrasonic imaging of blood flow in the anterior segment of the eye

PURPOSE. TO develop a noninvasive technique to visualize and measure blood flow in the iris and ciliary body. METHODS. Echo data from 50-MHz ultrasound scans of the iris and ciliary bod y of rabbits were digitized using a new "swept scan" modality. The method m akes use of spatial oversampling to identify regions with scatterers whose range changes with time. The data allowed construction of high-resolution B -mode images with embedded flow information. Pulsatility over the cardiac c ycle was evaluated by sending a series of pulses along a single line of sig ht containing a vessel of interest. Local blood flow and changes over the c ardiac cycle before and after application of atropine were quantified. RESULTS. Flow was identified in the radial vessels and major arterial circl e of the iris. Vessels with lumens as small as 40 mu m in diameter and Bow velocities as low as 0.6 mm/sec were measured. Change in blood velocity ove r the cardiac cycle was determined to be approximately 27%. Peak systolic v elocity after administration of topical atropine increased by 72%. CONCLUSIONS. This technique allowed visualization of flow using the same ty pe of very-high-frequency transducer now widely used for imaging the anteri or segment. The technique can also be used at lower frequencies for more po sterior tissues with similar improvement of resolution over Doppler. The ab ility to examine flow in the anterior segment of the eye offers a new tool for study of glaucoma, hypotony, tumors, and other disorders.