Aqueous Outflow System

It includes the trabecular meshwork, Schlemm’s canal,
collector channels, aqueous veins and the episcleral
veins (Fig. 9.3A).
1. Trabecular meshwork.It is a sieve-like structure
through which aqueous humour leaves the eye. It
consists of three portions.
i. Uveal meshwork. It is the innermost part of
trabecular meshwork and extends from the iris
root and ciliary body to the Schwalbe's line. The
arrangement of uveal trabecular bands create
openings of about 25 m to 75 m.
ii. Corneoscleral meshwork. It forms the larger
middle portion which extends from the scleral
spur to the lateral wall of the scleral sulcus. It
consists of sheets of trabeculae that are perforated
by elliptical openings which are smaller than
those in the uveal meshwork (5 μ-50 μ).
iii Juxtacanalicular (endothelial) meshwork. It
forms the outermost portion of meshwork and
consists of a layer of connective tissue lined on
either side by endothelium. This narrow part of
trabeculum connects the corneoscleral meshwork
with Schlemm’s canal. In fact the outer endothelial
layer of juxtacanalicular meshwork comprises the
inner wall of Schlemm’s canal. This part of
trabecular meshwork mainly offers the normal
resistance to aqueous outflow.

2. Schlemm’s canal. This is an endothelial lined oval
channel present circumferentially in the scleral sulcus.
The endothelial cells of its inner wall are irregular,
spindle-shaped and contain giant vacuoles. The outer
wall of the canal is lined by smooth flat cells and
contains the openings of collector channels.
3. Collector channels. These, also called intrascleral
aqueous vessels, are about 25-35 in number
and leave the Schlemm’s canal at oblique angles to
terminate into episcleral veins in a laminated fashion.
These intrascleral aqueous vessels can be divided
into two systems (Fig. 9.3A). The larger vessels
(aqueous veins) run a short intrascleral course and
terminate directly into episcleral veins (direct system).
Many smaller collector channels form an intrascleral
plexus before eventually going into episcleral veins
(indirect system).