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Raksha Urs, Jeffrey A Ketterling, Billy Y Yiu, Alfred Yu, Ioannis Michalopoulos, Lama Al-Aswad, Dana Blumberg, C Gustavo De Moraes, Jeffrey M Liebmann, George Cioffi, Ronald H Silverman; Determination of ocular blood-flow velocity by plane-wave ultrasound and correlation with ocular perfusion pressure. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5536.
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Impaired ocular blood-flow is believed to be a risk factor in glaucoma. While OCT-A is effective in imaging the vascular network in the retina and choroid, it does not quantify flow nor image the retrobulbar vessels supplying the eye. Plane-wave (PW) ultrasound offers a means for imaging flow dynamics in the choroid and retrobulbar vessels. In this report we describe pulsatile flow characteristics in the choroid, central retinal artery (CRA) and vein (CRV) and short posterior ciliary artery (SPCA) in a cohort of patients with primary open angle glaucoma (POAG).
We performed ultrafast PW imaging with a Verasonics Vantage 128 ultrasound system using an 18 MHz linear array probe. Choroidal imaging was performed in a horizontal plane just superior to the optic nerve at a frame rate of 1 kHz. For the major retrobulbar vessels, the optic nerve head region was imaged at 6 kHz frame rate. Imaging was performed twice for both eyes of 16 POAG patients. Fourier analysis produced spectrograms of flow velocity over the 3-second period of data acquisition. Peak systolic velocity (PSV), end diastolic velocity (EDV), resistive index (RI) and pulsatile index (PI) were determined and correlated with mean ocular perfusion pressure (MOPP=2/3×(MAP-IOP)) (MAP=mean arterial pressure, IOP=intraocular pressure).
IOP averaged 13.0±4.8 mmHg, MAP averaged 97.8±16.0 mmHg and MOPP averaged 56.4±10.4 mmHg over all eyes. MOPP was not significantly correlated with choroidal flow, but strongly correlated with PSV and EDV in the CRA (PSV: R=0.48, p=.006; EDV: R=0.47, p=.006) and CRV (PSV: R=0.56, p=.001; EDV: R=0.54, p=.002).
While flow velocities in the CRA and CRV were strongly correlated with MOPP, choroidal flow was not significantly altered, suggesting autoregulatory mechanisms. Although we did not find significant changes in the SPCA, this may be due to greater measurement uncertainty due to the variability of vessel orientation and hence velocity estimates due to uncertainty in the cosine correction term. PW ultrasound allows estimation of ocular flow velocities at intensity levels compliant with FDA guidelines. Measurement of MOPP and retrobulbar flow may prove a useful clinical parameter in glaucoma.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Directional power Doppler image of the optic nerve head region and spectrograms of central retinal artery and vein depicting flow-velocity variation as a function of time
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