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Hao F Zhang, Lisa Beckmann, Xian Zhang, Tsutomu Kume; Imaging the Entire Schlemm’s Canal with Visible-Light OCT and Visible-Light OCTA in Mouse. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4743. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The Schlemm’s canal (SC) is a key component of the conventional pathway for the removal of aqueous humor. The production and removal of aqueous humor controls the intraocular pressure (IOP), which is elevated in most glaucoma cases. The morphology of the SC can vary significantly within an individual, ranging from totally closed to a height of tens of microns. Its size has been shown to correlate with the presence and severity of glaucoma. Therefore, a tool allowing the visualization of the entire Schlemm’s canal in vivo can prove valuable. Here, we apply a visible-light OCT (vis-OCT) and vis-OCTA towards the study of the entire SC and the surrounding vascular network in mouse for the first time, providing micron-level axial resolution.
A custom-built vis-OCT system was designed to image the entire SC and its surrounding vessels. A pair of angled mirrors were mounted to a motorized rotational stage and placed at the end of the sample arm to deflect the incident light beam. The angle was optimized for image quality. Eight raster scans were acquired, each after a 45-degree rotation of the stage. Vis-OCTA images were also acquired by repeating each B-scan five times. Two methods of perturbing the natural state of the SC in wild-type mice were used: manometry to change the IOP and a suture tightened around the base of the eye to cause blood reflux into the SC.
Upon montaging all 8 raster scans, the entire area of the eye surrounding the SC was visualized, with the vessels clearly visible with OCTA (Fig 1). The SC was segmented from individual OCT B-scans. Differences in the SC could be clearly detected through both methods of perturbing the SC. Specifically, the SC increased in size with lower IOP and decreased in size with higher IOP. The suture tightened around the base of the eye clearly caused blood to enter the SC, which increased the optical scattering contrast in the SC and allowed it to be visualized with OCTA.
We developed a vis-OCT microscope system to image the entire SC area in vivo for mouse eyes. We demonstrated the micron level resolution and sensitivity of the system to detecting changes in the SC following various perturbations of the eye.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Fig. 1 Montage of OCTA showing vessels surrounding Schlemm’s canal
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