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Elizabeth Martin, Yi Jiang, Murray A Johnstone; Schlemm’s canal (SC) and Distal Aqueous Outflow Pathways: New scanning EM (SEM) Preparation Technique Permits Identifying Unique Structural Relationships.. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5683 - A0385.
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© ARVO (1962-2015); The Authors (2016-present)
To describe a new SEM protocol that permits exploring complex relationships between SC, collector channel ostia (CCO) and intrascleral collector channels running parallel to SC lumen (ISPC). The nature of the distal outflow system resistance remains uncertain and has been difficult to characterize with SEM because SC is normally little more than a potential space. We hypothesized that SC viscoelastic dilation, followed by frontal sections through the outflow system would provide an improved understanding of regional relationships.
Nemestrina monkey eyes (n=4), 31 limbal segments, Healon viscoelastic used to dilate SC, 150 µm cannula, micromanipulator. Frontal sections transected the outflow system. SEM after fixation, critical point drying, sputtering. Image analysis with Fiji. SC length, ISPC number and dimensions, number of CCO communicating with ISPC, CCO orientation relative to SC and ISPC were measured. Thickness of narrow scleral septum (NSS) separating SC and ISPC between CCO, the number of structures spanning directly between SC inner and outer wall (SSSC) as well as SSSC relationships to CCO and the septa between SC and ISPC were characterized.
Of the 31 segments, 16 (51.6%) segments had ISPC that coursed circumferentially parallel to SC. Mean SC length within segments was 1130 µm (446-2136µm, SD 586µm). Length of ISPC was 565µm (55-1520µm, SD 486µm), representing 50% of the length of SC. In the 16 segments with ISPC, 20 visible CCO were identified. CCO were arranged perpendicular to SC and ISPC. Mean CCO diameter was 67 µm (27-131µm, SD 36µm). NSS separated each of the ISPC from SC with a rather uniform diameter between ostia of 23µm, SD11µm. Eight segments had SSSC spanning between SC inner wall endothelium and SC external wall. Six of the eight SSSC were at or near CCO and attached to SC external wall at the CCO or in the region of the NSS between ISPC and SC.
Viscoelastic dilation of SC followed by frontal sectioning permitted exploring distal outflow pathway relationships. ISPC course circumferentially parallel to SC. In 4 eyes/16 segments, parallel ISPC encompassed 50% of SC length. CCO provided perpendicular communications between SC and ISPC. Pressure-dependent TM displacement, through tension on SSSC would also cause displacement of CCO origins and NSS that form one wall of ISPC.
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