2. Introduction
There are two segments in eye:
1. Anterior segment
2. Posterior segment
Anterior Segment
Anterior
chamber
-Contains
0.25 ml
aqueous
humour
Posterior
chamber
-Contains
0.06 ml
aqueous
humour
Posterior Segment
Structures posterior
to lens
-Vitreous humour,
- Retina
- Choroid
- Optic disc
3. -Lens divide eye into anterior and posterior segment
- From cornea to Iris is the Anterior chamber
- From Iris to Lens is the posterior chamber
- From Lens to Retina is the Posterior segment.
4. Aqueous humour
-It is a clear, colourless, watery
solution.
-Continuously Flows from posterior
to anterior chamber.
- This continuous circulation results
from a dynamic equilibrium.
5. Functions:
-Nutrition to lens, cornea and iris.
- Removes metabolically toxic products.
- Inflates globe and maintains IOP
- Facilitates cellular and humoral response of eye to
inflammation and infection.
- It serves as a mechanism to clear blood,
macrophages, remnants of lens matter and products
of inflammation from anterior chamber of eye.
- Provides optically clear medium for vision.
6. Physicochemical properties
Volume 0.31ml
(0.25 in anterior chamber
and
0.06 in posterior
chamber)
Refractive index 1.336
Density 1000kg/m3
Osmotic pressure 3-5 mOsm/l
pH 7.2
Rate of formation 2.3 µl/min
7. The blood-aqueous barrier
-Barrier to the movement of substances from plasma to
the aqueous humor.
-In the ciliary body the barriers include
Vascular endothelium
Stroma
Basement membrane
Pigmented and non-pigmented epithelium
- This is responsible for difference in chemical composition between plasma and
aqueous humor
8. Formation of Aqueous humour
-Aqueous humour is produced from pars
plicata along the crests of the ciliary
processes.
-It is derived from plasma within the
capillary network of the ciliary processes.
- Three physiological processes contribute to
the formation and chemical composition
of the aqueous humour:
1. Diffusion
2. Ultrafiltration
3. Active Transport
9. 1. Diffusion
-Diffusion is the movement of substance
across a membrane along
concentration gradient.
- As aqueous humour passes from PC to
Sclemm’s canal. It is in contact with
ciliary body, iris,
lens, vitreous, cornea, and trabecular
meshwork.
-There is diffusional exchange, so that
the AC aqueous humor resembles
plasma.
10. 2.Ultrafiltration
-The process by which fluid and its
solutes cross semipermeable
membrane under pressure gradient
is called ultrafiltration.
-As blood passes through capillaries
of the ciliary processes, about 4% of
the plasma filters through capillary
wall into the interstitial spaces
between the capillaries
and the ciliary epithelium.
11. 3. Active Transport
-Active transport is energy
-dependant process that
selectively moves substances
against its electrochemical
gradient across a cell membrane.
-It is postulated that majority of
aqueous humour formation
depends on active transport.
-It is done by non-pigmented
epithelial cells.
12. Steps of aqueous formation:
- The major factor in aqueous production approx
70% is active transport.
- Ultrafiltration accounts for 20% and diffusion 10%.
1. Formation
of stromal
pool
2. Active
transport of
stromal
filtrates
3.Passive
transport
across non-
pigmented
ciliary
epithelium
13. 1. Formation of stromal pool
-Most plasma substances
pass easily from the
capillaries of ciliary
processes, across the
stroma, and between the
pigmented epithelial cells
before accumulating
behind the tight junctions
of the nonpigmented
epithelium.
14. 2. Active transport of stromal filtrates
-Selective transcellular movement of certain
cations, anions and other substances across
the blood- aqueous barrier formed by the
tight junctions between the nonpigmented
epithelium.
-Aqueous humour secretion is mediated by
transferring NaCl from ciliary body
stroma to PC with water passively following.
15. -Other transported substances
include ascorbic acid, which is
secreted against a large
concentration gradient by the
sodium- dependant vitamin C
transporter.
-Carbonic anhydrase mediates the
transport of bicarbonate across
the ciliary epithelium through a
rapid interconversion between
HCO¯3 and CO 2
16. 3. Passive transport across non-pigmented
Ciliary epithelium
-Sodium is primarily responsible for movement
of water into posterior chamber and
its secretion is a major factor in the formation
of aqueous.
-Much of the evidence accumulated till now
indicates that the secretion of sodium into the
PC is the key event in aqueous formation.
17. The following evidence support
this view:
- Presence of large concentration
of Na - K - activated ATPase
especially at the lateral
interdigitations of the non-
pigmented epithelium.
- Oubian which is an inhibitor of
Na - K - activated ATPase
effectively reduces aqueous
formation.
- Shrinkage of ciliary processes is
inhibited by oubian.
18. Biochemistry of aqueous formation
-The structural basis for aqueous
humour secretion is the bilayered
ciliary epithelium.
(pigmented and non-pigmented
epithelium)
-The active process of aqueous
secretion is mediated by two
enzymes present in the NPE:
Na - K -ATPase and carbonic
anhydrase.
19. Aqueous humour dynamics
-Secreted by ciliary epithelium lining the ciliary processes.
- Enters the posterior chamber.
- It then flows around the lens and through the pupil into the AC
- There is convection flow of aqueous in the AC due to temperature
gradient.
- It leaves the eye by two pathways at the anterior chamber angle:
1.Trabecular or
conventional route.
2. Uveoscleral or
non conventional
route.
20. Trabecular
Meshwork
Inner wall of
sclemm’s canal
Into its lumen
Collector
channels
Aqueous
veins
Episcleral
venous
circulation
1.Trabecular Route
Iris root
Uveal meshwork
Anterior face of
ciliary muscle
Connective tissue
between muscle
bundles
Suprachoroidal
space and out
through sclera
2. Uveoscleral route
21.
22. Trabecular outflow accounts for 70% to 95% of the aqueous
outflow
And remaining 5% to 30% by uveoscleral outflow.
23. Cellular Organization of
Trabecular outflow pathway
-Scleral spur:
The posterior wall of the scleral
sulcus formed by a group of fibres,
the scleral roll, which run parallel to
the limbus and project inward to
form the scleral spur.
-Schwalbe Line:
Anterior to the apical portion of
the trabecular meshwork is a
smooth area called as zone S. The
posterior border is demarcated by
a discontinuous elevation, called
the Schwalbe line
24. Trabecular Meshwork:
The scleral sulcus is converted into a circular channel, called
the Schlemm canal, by the trabecular meshwork.
It may be divided into three portions:
a. Uveal Meshwork
-This innermost
portion is
adjacent to
aqueous humour
in the AC and is
arranged in
ropelike
trabecule that
extend from iris
root and ciliary
body to
peripheral
cornea.
b. Corneoscleral
Meshwork:
-This portion
extends from
the scleral spur
to the anterior
wall of the
scleral sulcus
c. Juxtacanalicular
Tissue:
- This structure
has three layers.
- The inner trabecular endothelial
layer is continuous with the
endothelium of corneoscleral
meshwork.
-The central connective tissue layer
and outermost portion is the inner
wall endothelium of the schlemm
canal
27. Cellular organization of the Uveoscleral Pathway
-Two unconventional pathways have been discriminated :
a. Through the anterior uvea at the iris root,
uveoscleral pathway
b. Through transfer of fluid into the iris vessels and
vortex veins, which has been described as
uveovortex outflow.
-The uveoscleral pathway is characterized as “pressure
independent”.
-It is reduced by cholinergic agonists, ageing, and is
enhanced by prostaglandin drugs.
-A potential explanation for the observed decline in
uveoscleral outflow with ageing is thickening of elastic
fibres in the ciliary muscles.
28. -Uveoscleral Outflow
-Studies have shown
aqueous humour passes
through the root of the iris
and interstitial spaces of the
ciliary muscle to reach the
suprachoroidal space.
- 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
substances of the sclera.
