Measuring retinal blood flow in rats using Doppler optical coherence tomography without knowing eyeball axial length.
OBJECTIVE
Doppler optical coherence tomography (OCT) is widely used for measuring retinal blood flow. Existing Doppler OCT methods require the eyeball axial length, in which empirical values are usually used. However, variations in the axial length can create a bias unaccounted for in the retinal blood flow measurement. The authors plan to develop a Doppler OCT method that can measure the total retinal blood flow rate without requiring the eyeball axial length.


METHODS
The authors measured the retinal blood flow rate using a dual-ring scanning protocol. The small and large scanning rings entered the eye at different incident angles (small ring: 4°; large ring: 6°), focused on different locations on the retina, and detected the projected velocities/phase shifts along the probing beams. The authors calculated the ratio of the projected velocities between the two rings, and then used this ratio to estimate absolute flow velocity. The authors tested this method in both Intralipid phantoms and in vivo rats.


RESULTS
In the Intralipid flow phantom experiments, the preset and measured flow rates were consistent with the coefficient of determination as 0.97. Linear fitting between preset and measured flow rates determined the fitting slope as 1.07 and the intercept as -0.28. In in vivo rat experiments, the measured average total retinal blood flow was 7.02 ± 0.31 μl/min among four wild-type rats. The authors' measured flow rates were consistent with results in the literature.


CONCLUSIONS
By using a dual-ring scanning protocol with carefully controlled incident angle difference between the two scanning rings in Doppler OCT, the authors demonstrated that it is feasible to measure the absolute retinal blood flow without knowing the eyeball axial length.
Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208.
Wenzhong
W
Liu
Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208.
Ji
J
Yi
Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208.
Siyu
S
Chen
Department of Biomedical Engineering, Florida International University, Miami, Florida 33174.
Shuliang
S
Jiao
Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208 and Department of Ophthalmology, Northwestern University, Chicago, Illinois 60611.
Hao F
HF
Zhang
D000818:Animals; D005123:Eye / Q000033:anatomy & histology*; D019047:Phantoms, Imaging; D051381:Rats; D012039:Regional Blood Flow; D012171:Retinal Vessels / Q000502:physiology*; D041623:Tomography, Optical Coherence / Q000379:methods*