Retinal, Choroidal, and Scleral Imaging by 1 Micrometer Band High-Penetraion Fourier Domain Oct and High-Contrast 3d Imaging of Choroidal Vasculature by Scattering Optical Coherence Angiography

Abstract

Purpose:: This paper demonstrates the three-dimensional (3D) in vivo imaging of the retina, choroids, and sclera of human subjects by custom-made high-penetration Fourier domain OCT (HP-OCT). A newly developed non-invasive high-contrast imaging method of 3D choroidal vasculature; scattering optical coherence angiography (S-OCA), is also demonstrated.

Methods:: The HP-OCT uses a swept-source OCT technique and 1 um band probe beam. The depth resolution is 11 um, and the maximum sensitivity is measured to be 101 dB with a probe power of 1.1 mW.The measurement speed of 28,000 A-scans/second enables 4.9 second or 2.5 second acquisition time for 3D retinal imaging with 512 (horizontal) times 256 (vertical) A-scans or 256 times 256 A-scans, respectively.A software-based contrast enhancement algorithm, S-OCA, was developed for improved contrast of 3D choroidal vasculature. The algorithm processes the 3D OCT intensity signal, and extracts only the regions of choroidal vessels by using an adaptive level-set method for each depth of the OCT volume.Three normal subjects were examined by the HP-OCT and S-OCA. This study was approved by the institutional board of University of Tsukuba.

Results:: Owing to the high-penetration property of the probing wavelength of 1 um, deep penetration to the sclera was observed with the two of the three subjects. Fringe artifacts in the OCT images, which are due to polarization rotation by the birefringence of collagen structures of the sclera, indicate that the penetration reaches to the sclera. To the best of our knowledge, this is the first demonstration of the visualization of the sclera of a normal eye by OCT.S-OCA algorithm reveals the 3D vasculature of in vivo human choroids clearly. S-OCA accompanied by a 3D skeletonizing visualization gaves us the details and intuitive understanding of the 3D structures of the vasculature. The three dimensional network structure and depth-resolved ICGA-like images of the choroidal vasculature are presented.

Conclusions:: The in vivo sclera of healthy subjects is firstly visualized by a custom made HP-OCT. S-OCA algorithm improved the contrast of the choroidal vasculature and gave us the 3D view of its network structure.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • image processing • sclera