In Vivo Multi-Level Vasculature Visualization in the Posterior Rodent Eye Using High Resolution Optical Coherence Tomography

Abstract

 

Purpose

 

To show the ability of using optical coherence tomography (OCT) for in-vivo imaging of the vasculature in rodents' posterior eyes. This technique enables long-term follow up studies of ophthalmic pathologies where morphological changes of the vasculature can be observed, e.g. age-related macular degeneration (AMD) or diabetic retinopathy (DR).

 

Methods

 

A custom-made high resolution polarization sensitive (PS-) OCT system was used to image the posterior eye of mice and rats. Three-dimensional images of different rats (Long-Evans, Brown Norway, Sprague-Dawley) and Black-6 mice were acquired. The healthy rodents were anaesthetized and scanned with an angle of 11x11° and 21x21° around the papilla. Increasing the signal-to-noise ratio was achieved by averaging 5 repeated B-scans at each B-scan position. Motion artifacts due to breathing/heart beat were compensated between adjacent B-frames. To visualize different layers of retinal and choroidal vasculature a semi-automatic segmentation of the retinal layers is performed in a first step. In a second step, the segmented layers are used to restrict the volume in which the expected vasculature is visualized. To show the retinal blood vessels between nerve fiber layer and inner nuclear layer a maximum intensity (reflectivity) projection is used. The smaller capillaries in the outer plexiform layer (OPL) are also visualized by a maximum intensity projection. To visualize the vasculature in the choroid an average intensity projection is used and the resulting map is inverted.

 

Results

 

The resulting vascular maps of each level show the ability of visualizing different vasculature structures. The first (most inner) projection shows big retinal vessels and nerve fibers around the optic nerve head. Smaller capillaries can be observed in the OPL. Visualizing choroidal vasculature is a more challenging task as the vessels appear as hollow structures in the images. These vessels appear unsharp although vascular structures are clearly visible. Projection artefacts (shadows) from larger vessels remain visible in deeper layers.

 

Conclusions

 

The combination of high resolution PS-OCT and intensity projections between certain levels enables to visualize retinal and choroidal vasculature. The resolution of the custom-made system is high enough to visualize retinal capillaries of rodents in the OPL by using only the reflectivity information.