Circumferential Flow in Schlemm's Canal

Moses, Robert A.

doi:10.1016/0002-9394(79)90519-1

Cited by 42 publications

(20 citation statements)

References 4 publications

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“…Imaging with 3D micro-CT also confirmed variability in collector channel orifice size in immersion fixed eyes (27 ± 5.0 µm compared to 5–50 µm (Dvorak-Theobald, 1955) and 50–70 µm (Rohen, Rentsch, 1968). Schlemm’s canal length of 33 mm in the immersed eye and 35 mm in the perfused eye was consistent with previous measurements of 36 mm in normal eyes (Moses, 1979). …”

Section: Discussionsupporting

confidence: 92%

Imaging the aqueous humor outflow pathway in human eyes by three-dimensional micro-computed tomography (3D micro-CT)

Hann

Bentley

Vercnocke

et al. 2011

Experimental Eye Research

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The site of outflow resistance leading to elevated intraocular pressure in primary open angle glaucoma is believed to be located in the region of Schlemm's canal inner wall endothelium, its basement membrane and the adjacent juxtacanalicular tissue. Evidence also suggests collector channels and intrascleral vessels may have a role in intraocular pressure in both normal and glaucoma eyes. Traditional imaging modalities limit the ability to view both proximal and distal portions of the trabecular outflow pathway as a single unit. In this study, we examined the effectiveness of three-dimensional micro-computed tomography (3D micro-CT) as a potential method to view the trabecular outflow pathway. Two normal human eyes were used: one immersion fixed in 4% paraformaldehyde, and one with anterior chamber perfusion at 10 mmHg followed by perfusion fixation in 4% paraformaldehyde/2% glutaraldehyde. Both eyes were postfixed in 1% osmium tetroxide, and scanned with 3D micro-CT at 2 µm or 5 µm voxel resolution. In the immersion fixed eye, 24 collector channels were identified with an average orifice size of 27.5 ± 5 µm. In comparison, the perfusion fixed eye had 29 collector channels with a mean orifice size of 40.5 ± 13 µm. Collector channels were not evenly dispersed around the circumference of the eye. There was no significant difference in the length of Schlemm's canal in the immersed versus the perfused eye (33.2 versus 35.1 mm). Structures, locations and size measurements identified by 3D micro-CT were confirmed by correlative light microscopy. These findings confirm 3D micro-CT can be used effectively for the non-invasive examination of the trabecular meshwork, Schlemm's canal, collector channels and intrascleral vasculature that comprise the distal outflow pathway. This imaging modality will be useful for noninvasive study of the role of the trabecular outflow pathway as a whole unit.

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Section: Discussionsupporting

confidence: 92%

Imaging the aqueous humor outflow pathway in human eyes by three-dimensional micro-computed tomography (3D micro-CT)

Hann

Bentley

Vercnocke

et al. 2011

Experimental Eye Research

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“…[23][24][25] Outflow resistance has been reported to be higher at higher levels of IOP. [26][27][28] One possible cause for increased resistance is collapse of the SC at higher pressures. 27,28 A similar numeric trend of higher resistance at higher perfusion pressures was seen in our study data as well (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…[26][27][28] One possible cause for increased resistance is collapse of the SC at higher pressures. 27,28 A similar numeric trend of higher resistance at higher perfusion pressures was seen in our study data as well (Fig. 5B); however, the difference between groups did not reach statistical significance.…”

Section: Discussionmentioning

confidence: 99%

A Novel 8-mm Schlemm's Canal Scaffold Reduces Outflow Resistance in a Human Anterior Segment Perfusion Model

Gulati

Fan

Hays

et al. 2013

Invest. Ophthalmol. Vis. Sci.

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PURPOSE.To study the effect on outflow facility and outflow resistance of a nitinol microstent implanted into Schlemm's canal.METHODS. Using a constant pressure perfusion method, outflow facility and outflow resistance were measured in 26 pairs of dissected anterior segments from donated human eyes. Measurements were made at perfusion pressures of 10, 20, 30 and 40 mm Hg. The Hydrus Microstent was placed in Schlemm's canal of one eye and the contralateral eye underwent a sham procedure. Outflow facility and outflow resistance were measured again after the microstent implantation or sham procedure.RESULTS. The Hydrus Microstent significantly increased outflow facility from 0.33 6 0.17 lL/min/mm Hg to 0.52 6 0.19 lL/ min/mm Hg (P < 0.001). Outflow resistance was significantly reduced from 4.38 6 3.03 mm Hg/lL/min at baseline to 2.34 6 1.04 mm Hg/lL/min (P < 0.001) with the microstent. There was a linear correlation between outflow resistance at baseline and decrease in outflow resistance with the microstent (R 2 ¼ 0.89, P < 0.0001).CONCLUSIONS. The increase in outflow facility and decrease in resistance supports the potential use of the Hydrus Microstent as a surgical option to reduce intraocular pressure (IOP). The IOP-lowering effect may be higher in eyes with higher outflow resistance (and IOP) as compared with eyes with lower outflow resistance (and IOP). (Invest Ophthalmol Vis Sci.

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“…Outflow facility ( c ) is expressed as a constant in the Goldmann equation, but in fact c decreases as IOP increases (Levene and Hyman 1969; Brubaker 1975), which has been attributed to collapse of Schlemm’s canal (Moses 1979; Van Buskirk 1982). In enucleated eyes, Brubaker (1975) measured a nonlinear relationship between outflow (Q) and IOP (Fig 4) consistent with an IOP-dependent decrease in outflow facility, which is defined Q /(IOP– P e ).…”

Section: Methods Of Measurementmentioning

confidence: 99%

Unconventional aqueous humor outflow: A review

Johnson

McLaren

Overby

2017

Experimental Eye Research

162

120

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Aqueous humor flows out of the eye primarily through the conventional outflow pathway that includes the trabecular meshwork and Schlemm's canal. However, a fraction of aqueous humor passes through an alternative or ‘unconventional’ route that includes the ciliary muscle, supraciliary and suprachoroidal spaces. From there, unconventional outflow may drain through two pathways: a uveoscleral pathway where aqueous drains across the sclera to be resorbed by orbital vessels, and a uveovortex pathway where aqueous humor enters the choroid to drain through the vortex veins. We review the anatomy, physiology and pharmacology of these pathways. We also discuss methods to determine unconventional outflow rate, including direct techniques that use radioactive or fluorescent tracers recovered from tissues in the unconventional pathway and indirect methods that estimate unconventional outflow based on total outflow over a range of pressures. Indirect methods are subject to a number of assumptions and generally give poor agreement with tracer measurements. We review the variety of animal models that have been used to study conventional and unconventional outflow. The mouse appears to be a promising model because it captures several aspects of conventional and unconventional outflow dynamics common to humans, although questions remain regarding the magnitude of unconventional outflow in mice. Finally, we review future directions. There is a clear need to develop improved methods for measuring unconventional outflow in both animals and humans.

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Circumferential Flow in Schlemm's Canal

Cited by 42 publications

References 4 publications

Imaging the aqueous humor outflow pathway in human eyes by three-dimensional micro-computed tomography (3D micro-CT)

Imaging the aqueous humor outflow pathway in human eyes by three-dimensional micro-computed tomography (3D micro-CT)

A Novel 8-mm Schlemm's Canal Scaffold Reduces Outflow Resistance in a Human Anterior Segment Perfusion Model

Unconventional aqueous humor outflow: A review

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