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Cheryl R. Hann, Andrew J. Vercnocke, Michael D. Bentley, Michael P. Fautsch; 3-Dimensional Analysis of Distal Outflow Pathways in POAG Eyes at Low and High Perfusion Pressures. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3273.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the distal outflow pathways of primary open angle glaucoma (POAG) and normal eyes perfused at low (10 mmHg) and high (20 mmHg) pressures.
Four pairs of human eyes (2 normal, ages 61 and 68 years; 2 POAG, ages 61 and 88 years) were obtained from the MN Lions Eye Bank. For each pair, eyes were perfused with phosphate buffered saline containing 5.5 mM glucose for 2 hours. One eye of each pair was perfused at 10 mmHg while the fellow eye was perfused at 20 mmHg. Eyes were fixed by anterior chamber exchange at like pressures with 4% paraformaldehyde/2% glutaraldehyde in 0.1 M phosphate followed by continuous perfusion with the same fixative for 8-12 hours. Quadrants were postfixed in osmium tetroxide, embedded in Epon Araldite, and scanned using 3-dimensional micro-computed tomography at 6 µm voxel resolution. Collector channels were enumerated and measured using ANALYZETM. Schlemm’s canal volume was measured in a stereology sub-program in ANALYZETM. Mean and standard deviation for each group was calculated.
At 10 mmHg, the number of identified collector channels were similar between POAG (4.6 ± 1.4 collector channels/quadrant) and normal eyes (4.8 ± 1.3 collector channels/quadrant). Collector channel orifice size was reduced in POAG (33.1 ± 11.9 µm) when compared to normal eyes (45.6 ± 12.1 µm). At 20 mmHg, the number of collector channels increased by 2.8-fold in normal (12.8 ± 6.7 collector channel/quadrant) and 2.0-fold in POAG eyes (9.0 ± 3.3 collector channel/quadrant). Collector channel orifice size was reduced by 24% in POAG eyes compared to normal eyes at both perfusion pressures. Schlemm's canal volume in POAG eyes was 3.2 fold (10 mmHg) and 2.4-fold (20 mmHg) smaller than normal eyes at comparable pressures. Occlusions, which were defined as thickened collector channel orifice walls, closure of collector channel, and/or flocculent material in Schlemm's canal adjacent to and blocking the collector channel orifices were observed 2.0-fold more frequently in POAG than normal eyes at 20 mmHg.
The distal outflow pathway of POAG eyes has reduced outflow area due to decreased Schlemm's canal volume, smaller collector channel orifice diameter and increased number of collector channel occlusions.
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