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Elizabeth Martin, Nicolette Orkney, Murray Johnstone; Microspheres (MS) Perfused into the Anterior Chamber (AC) enter the Lumen of Cylindrical Structures Spanning Schlemm’s canal (SC). Invest. Ophthalmol. Vis. Sci. 2013;54(15):3534.
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© ARVO (1962-2015); The Authors (2016-present)
Previous reports document cylindrical tube-like structures arising from funnel-shaped regions (F) of the inner wall of SC endothelium (SCE) to attain a cylindrical configuration, and then course across SC to attach to SC external wall. We hypothesized that these structures function as flow conduits and if so MS perfused into the AC will be carried into their lumen by flowing aqueous.
Nemestrina monkey eyes (n=14) Preliminarily perfusions with fluorescent MS; sizes: 15µm, 10µm, 8µm, 5µm, 2µm, 1µm. Final perfusions of 2µm (n=1) or 1µm MS (n=4) for mean of 23 min at mean IOP of 24 mmHg. SC dilation with Healon GV, a viscoelastic. Tissue fixed in 4% paraformaldehyde. Radial 250-500µm limbal segments cut. Segments evaluated with dissecting and fluorescent microscope for presence of cylindrical structures spanning SC. IHC using DAPI (20) or PI (7) for nuclei and CD31 for labeling of SC & CC endothelium(27). Imaging with confocal microscopy; processing with Fiji and Imaris.
No spheres present in tubes perfused at 15, 10, 8 or 5µm. In 1 eye perfused with 2 µm MS with 48 segments examined, MS were present in 2 (5%) of 40 tubes. In 4 eyes perfused with 1µm MS, 231 total segments were examined (Mean: 14.4 per quadrant). A total of 293 tubes were visualized (Mean: 18.3 tubes/quadrant, 1.27 tubes/segment). MS were present in 27 tubes (9.2% of total). Confocal imaging depth limitations resulted in regional tube image capture as follows: Of 27 tubes imaged, 8 spanned completely from SCE to SC external wall, 23/27 had both the funnel and the cylindrical region present, while 12/27 had a distal attachment of the tube to either the external wall of SC (6) or a septa at a collector channel ostia (CCO) (6). MS present in: funnel 17; cylindrical area 19; distal end 8; all three areas 2.
MS perfused into the AC are carried into the funnel and along the lumen of cylindrical tube-like structures arising from SC inner wall. Aqueous would not actively flow into and carry MS through a blindly ending tube without an outlet. One may reasonably conclude MS are carried into the lumen by actively flowing aqueous that passes into SC through the tubular conduits.
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