Evaluation of AO-OCT and pv-OCT for detailed study of blood flow in mouse retinal capillaries and vessels

Abstract

Purpose: To evaluate feasibility of Adaptive Optics - Optical Coherence Tomography (AO-OCT) and phase variance optical coherence tomography (pv-OCT) for non-invasive and label-free visualization and quantification of retinal and choroidal blood flow in mice in-vivo.

Methods: Two high resolution retinal imaging modalities AO-OCT and pv-OCT have been used to investigate retinal vasculature in mice. Both systems use the same high-speed acquisition Fourier-Domain OCT (FD-OCT) engine (132nm @ 855 nm broadband light source (Superlum) and CMOS camera (Basler) operating at 125,000 A-scan/s). The AO-OCT system uses Adaptive Optics to achieve improved lateral resolution while pv-OCT allows visualization of capillary bed morphology through calculation of the variance of local contrast between consecutive images. Several pigmented Wild Type (c57BL/6) and albino (BALB/cJ) mice, both strains from Jackson Laboratory, have been used as the imaging targets. During the imaging, mice were anesthetized with 2-3% inhalational isoflurane anesthetic. Pupils were dilated and cyclopleged with Tropicamide and Phenylephrine.

Results: The two techniques offered complementary views of mouse retinal vasculature. pv-OCT offered fast mapping of capillary bed morphology while speckle tracking in the AO-OCT volumes allowed quantitative evaluation of flow speed within capillaries. Application of pv-OCT allowed for label- free mapping of retinal microvasculature that could be later used as reference for imaging areas of interest with AO-OCT. The absence of pigmentation in the albino mice resulted in much improved visualization of the choroidal vasculature.

Conclusions: Application of two distinct but related OCT imaging modalities enables a more comprehensive study and evaluation of retinal and choroidal vasculature. As evaluation of retinal and choroidal vasculature in vivo with standard Fluorescein Angiography is impractical due to contrast degradation by scleral scattering, the application of OCT based vasculature imaging methods provides a useful alternative for detailed study of the choroidal vasculature morphology and flow of albino strains.

Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 688 retina • 452 choroid