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Yohko Murakami, Siamak Yousefi, Amir Marvasti, Christopher Bowd, Robert N Weinreb, Alex S Huang; Visualization of Aqueous Outflow Structures with Spectralis Spectral-Domain Optical Coherence Tomography in the Living Human Eye. Invest. Ophthalmol. Vis. Sci. 2014;55(13):927.
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© ARVO (1962-2015); The Authors (2016-present)
To demonstrate noninvasive visualization of aqueous outflow (AO) structures in the living human eye in two (2D) and three (3D) dimensions using the commercially available Spectralis spectral-domain optical coherence tomographer (SD-OCT).
AO structures, including Schlemm’s canal (SC) and collector channels (CC) of both eyes, were imaged by SD-OCT (Spectralis; Heidelberg Engineering) during one setting in a healthy subject. The panning camera head coupled with TruTrack active eye tracking and simultaneous dual-beam imaging allowed for maintained and optimal 360 degree radial orientation of OCT scans during image acquisition. To enhance image quality and diminish noise, frame-averaged mean images were created with the Automatic Real Time (ART; 8) mean function. Twelve volume scans (161 B-scans; 10 x 15 degree scan angle covering a 5.5 x 8.3 mm region at the limbus) using the anterior segment module on high-resolution setting were obtained centered on each clock hour. Axial resolution of each A-scan was 3.9 um with a lateral resolution of 11 um and distance between B-scans of 35 um. In one clock hour, for each 2D slice, the tissue was discriminated from noise, and SC was detected based on intensity distribution (lower intensity values compared to nearby tissue) and location (in the vicinity of intersection of sclera and iris). Then CC and outflow pathways were detected based on intensity distribution. All identified SC, CC, and outflow pathways regions were fused to create 2-D object slices (Matlab; Mathworks). This information was then compiled as a stack with cropping, re-sizing, surface mapping polygonal reconstruction, and 3D manipulation (Imaris; Bitplane).
SC and CC were readily visible on both the 2D (Figure 1; red box = region of interest; blue boxes depict automated detection of SC and CC) and 3D (Figure 2) images. The 3D image also provided visualization of SC discontinuations. CC branching directly from SC could be visualized with downstream Y-shaped aqueous veins noted.
We present visualization of AO structures in the living human eye using the Spectralis and demonstrate the possibility of 3D reconstruction from conventional 2D images.
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