3. Schwalbe's Line
• Just anterior to the
apical portion of the
trabecular meshwork
is a smooth area
called as zone S.
• It varies in width from
50 to150 μm .

4. This anterior border of
this zone marks
transition from
1. trabecular to corneal
endothelium
2. termination of t he
Descemet’s membrane
3. Insertion of trabecular
meshwork into corneal
stroma.

5. • The posterior border is demarcated by a
discontinuous elevation, called
Schwalbe's line, formed by the oblique
insertion of uveal trabeculae into limbal
stroma.
• Secretory cells, called Schwalbe’s line
cells, produce a phospholipid material that
facilitates aqueous humor flow through the
canalicular system.

6. Scleral Spur
• It is a fibrous ring projecting
from inner aspect of
anterior sclera which runs
parallel to the limbus
• Attached
 anteriorly : trabecular meshwork
 posteriorly : sclera and longitudinal fibers of ciliary
muscle.
• varicose axons characteristic of mechanoreceptor
nerve measure stress in the scleral spur due to
ciliary muscle contraction or changes in IOP.

7. Trabecular Meshwork
Trabecular meshwork is a sieve like structure
bridging scleral sulcus and converts it into
Schlemm’s canal
It is divided into three portions:
(a) uveal meshwork,
(b) corneoscleral
meshwork, and
(c) juxtacanalicular tissue

8. Uveal Meshwork
• This inner most portion is
adjacent to the aqueous humor
in the anterior chamber
• It is arranged in cord or rope like
trabeculae that extend from the
iris root to the Schwalbe's line .
• The arrangement of the
trabecular bands creates
irregular openings that vary in
size from 25 to 75 μm.

9. Corneoscleral Meshwork
• This portion extends
from the scleral spur
to the anterior wall
of the scleral sulcus
• It consists of 8-14
sheets of trabeculae
that are
interconnected via
cytoplasmic
processes.

10. They are perforated by
elliptical openings which
become progressively
smaller as the trabecular
sheets approach
Schlemm's canal .
• These perforations are not aligned and have
a diameter ranging from 5 to 50 μm

11. • The anterior tendons of the
longitudinal ciliary muscle
fibers insert on the scleral
spur and posterior portion of
the corneoscleral meshwork.
• This anatomic arrangement
suggests an important
mechanical role for the
cholinergic innervation of
ciliary muscle on trabecular
meshwork function

13. Ultrastructure of Meshwork
• Both the uveal and corneoscleral trabecular bands
or sheets are composed of four concentric layers
1. An inner connective tissue core is composed of
collagen fibers, with 64nm periodicity. The central core
contains collagen types I and III and elastin.
2. Elastic fibers are arranged in a spiraling pattern with
periodicity of 100nm.

14. 3. Cortical zone also called as glassy membrane
4. An outer endothelial layer provides a continuous
covering over the trabeculae

15. Juxtacanalicular Tissue
The outermost portion of the meshwork (adjacent to Schlemm's
canal)
This structure has three layers consisting of a layer of connective
tissue lined on either side by endothelium
The inner trabecular endothelial layer is continuous with the
endothelium of the corneoscleral meshwork

16. The central connective tissue layer has variable thickness and is
unfenestrated with several layers of parallel, spindle shaped cells
loosely arranged in a connective tissue ground substance.
The outermost portion of the trabecular meshwork is the inner wall
endothelium of Schlemm's canal.
This endothelial layer has significant morphologic characteristics,
which distinguish it from the rest of the endothelium in both the
trabecular meshwork and in Schlemm's canal.

17. Schlemm's Canal
This 360-degree endothelial-lined channel
It is a single channel but occasionally
branches into a plexus-like system .

18. The endothelium of the outer
wall is a single cell layer that
is continuous with the inner
wall endothelium but has a
smoother surface with larger,
less numerous cells and no
pores .
The outer wall also differs in
having numerous, large outlet
channels

19. Lip-like thickenings are present around the openings of
the outlet channels and septa are noted to extend from
these openings to the inner wall of Schlemm's canal,
which help keep the canal open.

20. Collector channels
• Schlemm's canal is connected
to episcleral and conjunctival
veins by a complex system of
intrascleral channels.
• Two systems of intrascleral
channels have been identified:
(a) An indirect system of
numerous(15-20), finer
channels, which form an
intrascleral plexus
before eventually draining into
the episcleral venous system
and

21. (b) A direct system of large
caliber vessels, which run a
short intrascleral course and
drain directly into the episcleral
venous system, they are about
6-8 in number and also called
as aqueous.
• However, others refer to the
proximal, or intrascleral,
portion of these vessels as
outflow channels because the
structural pattern of the outer
wall of Schlemm's
canal extends into the first third
of these channels

22. Episcleral and Conjunctival
Veins
The aqueous vessels join the episcleral and conjunctival
venous systems by several routes.
Most aqueous vessels are directed posteriorly, with most
of these draining into episcleral veins, whereas a few
cross the subconjunctival tissue and drain into
conjunctival veins.

23. The episcleral veins drain into the cavernous sinus via
the anterior ciliary and superior ophthalmic veins,
while the conjunctival veins drain into superior
ophthalmic or facial veins via the palpebral and angular
veins .

24. Trabecular Outflow
It is the main outlet (85-95%) for aqueous humor.
Various mechanisms described for aqueous transport
are:
• Vacuolation theory
• Sonderman’s channels
• Contractile microfilaments
• Endothelial pores

25. Vacuolation theory

26. Vesicles and large vacuoles are seen in
endothelium.
These vacuoles open and close
intermittently to transport aqueous
This is a pressure dependent passive
transport as no. and size of pores increase
with increase in IOP.

27. Uveoscleral Outflow
It accounts for 5-15% of total aqueous drainage.
It increases with increase in IOP until IOP is equal to episcleral
venous pressure, thereafter it is independent of IOP.
Aqueous humor passes through the root of the iris and interstitial
spaces of the ciliary muscle to reach the suprachoroidal space.

28. From there it passes to episcleral tissue via scleral pores
surrounding ciliary blood vessels and nerves, vessels of optic
nerve membranes, or directly through the collagen substance
of the sclera.
A lower hydrostatic pressure is present in the suprachoroidal
space than in the anterior chamber and this pressure
difference is the driving force for uveoscleral outflow.
The main resistance to uveoscleral outflow is the tone of
ciliary muscle