Abstract
Purpose: :
To measure the effect of glaucoma on the retinal blood flow.
Methods: :
A Doppler Fourier-domain optical coherence tomography (FD-OCT) system with an axial resolution of 4.6 µm, speed of 4.2 frames/second and minimal detectable Doppler shift of 51 Hz (0.016 mm/s) was used. A double circular scan around the optic nerve head was used to measure the axial blood flow velocity profile and determine the incident angle between the blood vessel and the scanning beam. The total flow velocity was computed from the axial velocity component and the angle. Volumetric flow in the branch retinal venules was summed to obtain the total retinal blood flow. The flow was averaged over 8 frames in 2 seconds. Measurements were performed 8 times in the right eye of each human subject.
Results: :
The total retinal blood flow was measured in 10 glaucoma patients and 7 normal subjects. The normal retinal flow was between 27.5 to 36 µl/minute. The retinal flow for glaucoma patients was between 16.1 to 27.8 µl/minute. The retinal flow of glaucoma patients was lower than that of normal subjects (p < 0.0009). Retinal blood flow was highly correlated with visual field parameters in glaucoma patients.
Conclusions: :
We describe a new method for measuring the total retinal blood flow in glaucoma patients with FD-OCT that requires only a few seconds for each measurement. Unlike other methods for retinal blow flow measurement, our technique did not require any assumptions on vessel geometry or flow profile. And the measurements are provided in absolute units. Glaucoma decreases the retinal blood flow in proportion to its severity. Doppler OCT measurement of retinal blood flow may be useful in the diagnosis and staging of glaucoma, and may have prognostic value.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • blood supply • image processing