Because of their oblique orientation, in single sections septa some­ times appear to be attached to Schlemm’s canal posterior wall, but suspended unattached in Schlemm’s canal anteriorly.15 Septa are composed of dense parallel collagen bundles that are continuous with and have staining characteristics identical to collagen bun­

dles of the sclera.15 The septa typically join the collagenous walls of the canal rather than attaching to the trabecular meshwork.15,139

Although the canal is occasionally separated into channels, it is usually a single lumen.139 Collector channels are at times quite large (50–70 micron) and course circumferentially adjacent to the canal for a considerable distance.87,139 In individual histologic sec­ tions, collagenous partitions between large collector channels and

Schlemm’s canal may be confused with septa within the canal and thus appear to divide the canal into more than one channel.87,139

Schlemm’s canal valves spanning across Schlemm’s canal

Schlemm’s canal valves arise from the inner wall endothelium of

Schlemm’s canal, develop a cylindrical configuration and course across the canal to attach to the external wall (Fig. 3-9).15,73,78,140–142 The

valve walls are continuous with Schlemm’s canal inner wall endothe­

lium as documented by light, scanning, and transmission electron microscopy.15,73,78,140,141 Laboratory evidence of a lumen continuous

with the juxtacanalicular space consists of studies with the dissecting,

light, scanning, and transmission electron microscope.15,73,140–143 Tracer studies demonstrate a communication between the anterior chamber and Schlemm’s canal through the lumen of the structures using both antegrade and retrograde techniques.15,141 Pigment gran­ ules and amorphous extracellular matrix material are present in the

lumen of the aqueous valves, a finding like that in the juxtacanalicu­ lar space.15,73,78,140–142 The valve walls distend and recoil in response to changes in IOP (see Fig. 3 9).15,140 The presence of Schlemm’s

canal valves is documented at the operating microscope in liv­ ing human eyes during Schlemm’s canal surgery.15 In vivo, aqueous enters Schlemm’s canal in a pulsatile fashion through structures with a size and configuration like those characterized in the laboratory (see Fig. 3-9).15 Functionally, the aqueous valves have been proposed

as part of a mechanical pump discharging aqueous to Schlemm’s canal.15,140 The lumen of the valves is compressed between the walls

of Schlemm’s canal at a relatively low IOP of 25 mmHg.78

Herniations or protrusions of Schlemm’s canal inner wall

As the inner wall endothelium of Schlemm’s canal distends outward

in response to pressure, the distending endothelial wall forms pro­ jections, herniations or protrusions into Schlemm’s canal.27,28,72,79, 89,96,140 These protrusions do not attach between the walls of the

canal, and the distention is completely reversible with movement