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

Abstract

We present in vivo human total retinal blood flow measurements using Doppler Fourier domain optical coherence tomography (OCT). The scan pattern consisted of two concentric circles around the optic nerve head, transecting all retinal branch arteries and veins. The relative positions of each blood vessel in the two OCT conic cross sections were measured and used to determine the angle between the OCT beam and the vessel. The measured angle and the Doppler shift profile were used to compute blood flow in the blood vessel. The flows in the branch veins was summed to give the total retinal blood flow at one time point. Each measurement of total retinal blood flow was completed within 2 s and averaged. The total retinal venous flow was measured in one eye each of two volunteers. The results were 52.90+/-2.75 and 45.23+/-3.18 microlmin, respectively. Volumetric flow rate positively correlated with vessel diameter. This new technique may be useful in the diagnosis and treatment of optic nerve and retinal diseases that are associated with poor blood flow, such as glaucoma and diabetic retinopathy.

Fig. 1

Circular scan pattern of FD-OCT sampling beam. (a) The circular retinal OCT scan beam rotates in a cone pattern. The apex of the cone is the nodal point of the eye. (b) The cylindrical OCT image is unfolded to fit a rectangular display where the horizontal axis corresponds to the scanning angle from 0 to 360 deg. The vertical axis corresponds to the depth dimension along the axis of beam propagation.

Fig. 2

Three-dimensional diagram of the OCT beam scanning in a circular pattern across the retina. Two scanning radii, r₁ and r₂, are shown in this diagram. See text for symbols.

Fig. 3

The angle β between the OCT plane S_o and the plane normal to the flow direction P_v is indicated. Generation of a Doppler signal depends upon the FD-OCT plane S_o, which crosses the blood vessel, being different from plane P_v, which is normal to the direction of blood flow.

Fig. 4

Path of the scanning beam in the double circular scanning pattern. For vessel V_S, the scanning length was 1 mm.

Fig. 5

Doppler OCT images with grayscale display of the Doppler frequency shift. The horizontal axis shows the scanning angle from 0 to 360 deg. (a) Circular scan at a radius of 1.8 mm; (b) circular scan at 2.0-mm radius. Retinal branch veins are labeled from V₁ to V₇. The inset window shows vessel V₄ as an example of background signal removal.

Fig. 6

Influence of sampling step on the measured volume of blood flow. For sampling steps greater that 1.4 μm, the estimate of blood flow decreased.

Fig. 7

Correction of the Doppler noise due to background motion. The solid curve shows the original signal. The dashed curve shows the Doppler signal after background removal.

Fig. 8

Normalized peak flow speed variation with time for the vessel V₁ shown in Fig. 6.

Fig. 9

Relationship between vessel diameter and volume blood flow.

Fig. 10

Repeatibility measurement for the second subject.