Retinal blood flow measurement by circumpapillary Fourier domain Doppler optical coherence tomography

Abstract

Optical coherence tomography (OCT)¹ provides high-resolution cross-sectional imaging^{2, 3, 4, 5, 6} and is commonly used in the diagnosis and management of retinal diseases^{7, 8, 9} and glaucoma.^{10, 11} In addition to obtaining morphological images, OCT can also detect a Doppler shift of reflected light, which provides information about flow and movement.^{12, 13, 14} Several investigators have studied the visualization of blood flow and flow dynamics using Doppler OCT,^{15, 16, 17, 18, 19} but the measurement of the total flow velocity and volume requires additional information about the incident angle between the OCT probe beam and the blood vessel. This information is not available within a single cross-sectional OCT image. Determination of the incident angle requires three-dimensional (3-D) imaging of the blood vessel using more than one cross-sectional scan. Measurement of flow in branch retinal vessels in vivo has recently been accomplished using Doppler Fourier domain OCT (FD-OCT).^{20, 21} Phantom flow measurements showed²² that the difference between the measured flow and actual flow is less than 10%. However, sequentially imaging each retinal blood vessel is time-consuming and not a practical way of measuring the total retinal perfusion in a clinical setting. It is desirable to measure the total retinal blood flow in a single scan. Three-dimensional circular scan imaging has been proposed as a method for measuring retinal blood flow.²³ However, 3-D imaging of the peripapillary area requires many seconds and cardiac cycles, and the measurement of several flow values within a cardiac cycle was demonstrated for an arc scan across only two vessels.²³