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Ronald H Silverman, Raksha Urs, Harriet O Lloyd, Jeffrey Ketterling, Billy Yiu, Alfred Yu; Ultrasound Imaging and Measurement of Choroidal Flow. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4673.
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© ARVO (1962-2015); The Authors (2016-present)
We developed ultrafast plane-wave ultrasound methods that allow imaging of ocular anatomy and blood flow, including spectrograms depicting flow velocity at any image position over the cardiac cycle. Littile is known regarding choroidal flow dynamics, and in this study, we imaged and characterized choroidal flow in normal subjects.
We implemented ultrafast plane-wave imaging on a Verasonics Vantage 128 ultrasound system using an 18 MHz linear array probe with 128 elements. Imaging was performed in a horizontal plane just superior to the optic nerve. Ten plane-wave transmissions were made over an angle range of ±9o and added coherently to form 1000 compound images/sec. Both eyes of 8 normal subjects were scanned 3 times in one examination. A singular value decomposition filter was used in combination with a 10 Hz high-pass filter to suppress signals originating from stationary and slowly moving tissue. Fourier analysis of the filtered data produced a spectrogram plot choroidal flow velocity over the 3-second period of data acquisition. Peak systolic velocity (PSV) and end-diastolic velocity (EDV) were determined and resistive Index (RI) calculated as (PSV-EDV)/PSV.
In power Doppler images, choroidal flow appeared as an unresolved background component with resolved arterioles oriented roughly in a posterior-to-anterior direction, but progressively more oblique with lateral distance from the ONH. PSV averaged 10.07±2.11 mm/sec OD and 9.88±2.88 mm/sec OS. ANOVA repeated measures showed the standard deviation within triplicate measurements of PSV to be 2.02 mm/sec. RI averaged 0.50±0.13 OD and 0.51±0.19 OS. ANOVA showed no significant difference in PSV or RI between left and right eyes, but significant (p<.001) variation among subjects.
In this report, we demonstrated imaging and measurement of choroidal flow velocity over the cardiac cycle in normal subjects. Choroidal PSV was found to be significantly slower than that which we previously measured in short posterior ciliary artery (~80 mm/sec). Although there is a pulsatile component to choroidal flow, this was significantly less than in the ciliary artery (where RI≈0.6). We will further extend this database of normal subjects as a basis for comparison to flow measurements in pathologic conditions such as glaucoma.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Left: Power Doppler image depicting choroidal flow. Right: Spectrogram depicting mean choroidal flow velocity over a 3 second period.
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