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R.H. Silverman, D. Kruse, K.W. Ferrara, J. Cannata, K.K. Shung, A. Chabi, D.J. Coleman; Visualization of Blood-Flow in the Ciliary Processes with High-Frequency Ultrasound . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3610.
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Purpose: The non-pigmented epithelium of the ciliary processes is the site of aqueous fluid production. The metabolic requirements of this action dictate a rich microvascular blood supply. Ciliary process perfusion, however, is in the form of a capillary network with slow-flow conditions that is not amenable to imaging using conventional techniques such color-flow Doppler. We developed high-frequency ultrasound systems using PVDF transducers and signal processing methodologies that allowed visualization of slow flow. We previously descibed slow-flow in the major arterial circle and meridional vessels of the iris, but flow in the processes of the ciliary body was difficult to detect. Improvements in transducer technology have now provided increases in sensitivity allowing visualization of flow in the ciliary processes. Methods: We scanned a series of rabbit (NZW) eyes using a transducer with a lithium niobate piezoelectric element with a 40 MHz center frequency, a 6 mm aperture and 12 mm focal length. Scanning was accomplished using a fluid standoff contained in a polyethylene membrane and coupled to the eye with methylcellulose. With the focus placed in the region of the ciliary body, swept-mode data were acquired. Each scan consisted of 1024 vectors spaced 2 microns apart, with radiofrequency echo data acquired at a 250 MHz sample rate. Following acquisition, adjacent vectors were aligned, a Wall filter used to isolate regions of flow from clutter (stationary tissue structures), and color-flow images produced. Results: Images readily demonstrated flow in the iris stroma, the major arterial circle, and in the ciliary processes. Vascular connections between the iris and iridal processes were demonstrable. Flow was detectable with velocities of less than 5 mm/sec and in vessels down to the resolvable limits of the transducer. Conclusions: We have demonstrated the ability to visualize and measure flow in the ciliary processes. This capability may have direct applicability to increasing our understanding of disease states such as hypotony, glaucoma and uveitis, and in measurement of the effects of medications on ciliary body perfusion in a non-invasive manner.
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