Total retinal blood flow measurement in the human eye with 3-Beam Doppler Optical Coherence Tomography

Abstract

 

Purpose

 

To measure the total retinal blood flow and obtain flow/velocity profiles within all major retinal vessels originating from the optic nerve head (ONH) using an improved three-beam Doppler OCT (D-)OCT technique.

 

Methods

 

The three beam D-OCT consists of three independent superluminescent diode (SLD) sources with a central wavelength of 840 nm and a spectral bandwidth of 50 nm. The collimated exiting beams share a common bulk optics Michelson interferometer. A well-defined beam geometry enables the full reconstruction of the three dimensional velocity vector, without prior knowledge on the vessel geometry, which is normally required for D-OCT systems with less than three beams.<br /> In the sample arm a custom made facet prism telescope allows for variable beam separation adjustment without alteration of the beam diameter. In conjunction with a normal telescope a transversal resolution of approximately 30 µm is achieved.<br /> A two axis gimbal less MEMS mirror allows raster, circular and resonant scan patterns, which are not practical with a classical 2 axis galvo scanner, because of heavy beam movement at the pupil of the eye, caused by off-pivot point scanning.<br /> Eyes of healthy subjects were imaged and the mean total retinal blood flow as well as the velocity profiles inside all major retinal vessels emerging from the ONH were extracted.

 

Results

 

Figure 1 shows an example of a circular scan around the ONH of a healthy human subject. The velocity profiles of all major vessels are visible. Furthermore 3 beam D-OCT allows the reconstruction of the vessel geometry, showing excellent agreement between the actual and calculated vessel orientation as well as the flow direction. The total venous mean flow was 54.7 µl/min, while the total arterial flow was 47.8 µl/min.

 

Conclusions

 

The improved three beam D-OCT technique allows the direct measurement of total retinal blood flow as well as velocity vector determination with various scan patterns independent from any a-priory knowledge on the vessel geometry. With further development the technique may aid the early diagnosis of eye diseases like glaucoma.