Ophthalmology

1. AQUEOUS HUMOUR DYNAMICS
Dr. Ankit Bista
1st year resident
Ophthalmology Department

2. OUTLINE
 Introduction
 Functions
 Physiological properties
 Composition
 Anatomy
 Aqueous formation
 Aqueous outflow

3. INTRODUCTION
 Aqueous is a thin, watery fluid that fills the
space between the cornea and the iris (anterior
chamber).
 Aqueous humour dynamics plays an important
role in development of pathophysiological
mechanism of Glaucoma.

5. FUNCTIONS
 Maintains the intraocular pressure.
 Provides nutrition (e.g. amino acids and
glucose).
 Carries away waste products.
 Transports ascorbate in the anterior segment to
act as an anti-oxidant agent.
 Presence of immunoglobulin indicates a role in

6. PHYSIOLOGICAL
PROPERTIES
 Volume 0.31ml (0.25 ml in anterior chamber and
0.06 ml in posterior chamber)
 Refractive index 1.333
 PH 7.2
 Hyper osmotic
 Rate of formation 2.0 to 3.0 μl/min

7. COMPOSITIONS
 Water: 99%
 Proteins: 5-16 mg/ 100ml
 Na+, HCO3
+, Cl-
 Amino Acids
 Ascorbate, Pyruvate and Lactate
 Urea and Glucose
 Prostaglandin and Cyclic- AMP

8. Anterior chamber Posterior
chamber
HCO3 Low High
Cl High Low
Ascorbate Low High

9. DYNAMICS
 Anatomy of the structures involving aqueous
humour formation and drainage
 Aqueous humour formation
 Aqueous humour drainage

10. ANATOMY
Primary ocular structures involved are:
 Ciliary body
 Posterior chamber
 Anterior chamber
 Angle of anterior chamber
 Aqueous outflow system

12. CILIARY BODY
 Site of aqueous production
 Triangular in shape
 Outer side- lies against the sclera with a supra
choroidal space in between
 Inner side of ciliary body has two parts
A) Anteriorly- pars plicata (finger like ciliary process)
B) Posteriorly- pars plana

14.  Ciliary muscle- non striated muscle - three parts
1. Longitudinal or meridional fibers- helps in
aqueous outflow and accomodation
2. Circular muscles- helps in accomodation
3. Radial or oblique fibers- helps in accomodation
CLINICAL CORRELATION
Pilocarpine, acts at parasympathetic muscarinic receptor site to cause ciliary
muscle spasm and pupillary miosis.
Contraction of the ciliary muscle produces traction on the trabecular meshwork,
facilitating aqueous humour drainage and lowering IOP.

16. CILIARY PROCESSES
 70-80 whitish finger like projections
 Composed of double layer epithelium over a
core of stroma and a rich supply of fenestrated
capillaries.
 Apical surface of inner non-pigmented
epithelium (NPE) and outer pigmented
epithelium (PE) are joined by tight junctions
which contributes to Blood- Aqueous barrier.

19. Vascular Supply of Ciliary Body
 The major arterial circle, which is formed by
anastomosis between the long posterior ciliary
artery and anterior ciliary arteries.
CLINICAL CORRELATION
Brimonidine, an α- adrenergic agonist commonly used for glaucoma treatment,
reduces aqueous formation by causing vasoconstriction of ciliary arterial supply.

21. POSTERIOR CHAMBER
 Triangular space
 0.06 ml of aqueous humour
 Boundaries:
Anterior : Posterior surface of iris and part of
ciliary body
Posterior : Crystalline lens and zonules
Lateral : Ciliary body

22. ANGLE OF ANTERIOR
CHAMBER
Structures forming angle of anterior chamber:
 Ciliary band
 Scleral spur
 Trabecular meshwork
 Schwalbe’s line.

23. CILIARY BAND
 Most posterior landmark in angle recess which
is viewed as a dark band on gonioscopy
 Represents the anterior face of ciliary body
including insertion of ciliary muscle into scleral
spur

24. SCLERAL SPUR
 Pale, translucent narrow strip of scleral tissue
 Marks the posterior boundary of scleral sulcus

25. TRABECULAR MESHWORK
 Broad band of tissue extending from Scleral
Spur to Schwalbe’s Line
 No pigmentation at birth but develops pigment
with increasing age.
CLINICAL CORRELATION
Some pathological conditions can cause increased pigmentation like:
• Pseudo exfoliation syndrome
• Pigment dispersion syndrome

26. SCHWALBE’S LINE
 Anterior limit of the drainage angle
 Seen as fine scalloped border at the
termination of Descemet’s Membrane of
cornea
CLINICAL CORRELATION
In 15-20% of normal subjects, it may be hypertrophied and project as thin,
glistening ridge in Anterior Chamber.This condition is known as Posterior
Embryotoxon.

27. SHAFFERS SYSTEM OF
GRADING

28. ANTERIOR CHAMBER
 2.5-3 mm deep in centre
 Contains 0.25ml of aqueous humour
 Boundaries:
Anterior- Posterior surface of cornea,
Posterior- Anterior surface of ciliary body and
iris
 Communicates with posterior chamber through

29. AQUEOUS FORMATION
 Ciliary processes are the main site of aqueous
humour production.
 Mainly by thee mechanisms:
1. Ultrafiltration-20%
2. Active secretion-70%
3. Diffusion-10%

30. ULTRAFILTRATION
 Process by which fluids and its solutes crosses
semipermeable membrane under pressure
gradient.
 Favored by hydrostatic pressure difference
between the capillary pressure and the
interstitial fluid pressure.
 Resisted by the pressure difference between
oncotic pressure of plasma and aqueous

31.  Ultra filtration helps to move fluid out of the
capillaries into the stroma but alone is
insufficient to account for volume of fluid moved
into the posterior chamber.

32. ACTIVE TRANSPORT
 Energy dependent process.
 Selective movement of a substance against its
electrochemical gradient across a cell-
membrane.
 Depends on ion/s being actively secreted into
inter-cellular clefts of non-pigmented epithelial
cells beyond tight junctions.

33.  Main ions to be actively transported across the
non-pigmented epithelium include Sodium,
Chloride, Bicarbonate
 Active transport of Na+ is the key feature of
aqueous production

34. DIFFUSION
 Passive movement of ions across a membrane
along its concentration gradient.
 Lipid soluble substances are transported by
diffusion through the lipid portions of the cell
membrane of the ciliary processes.

35. STEPS OF AQUEOUS
FORMATION
 Formation of stromal pool
 Active transport of stromal filtrates
 Passive transport across non-pigmented ciliary
epithelium

36. AQUEOUS DRAINAGE
SYSTEM
Trabecular
Meshwork
Schlemm’s Canal
Collector Channels
Episcleral Veins

37. TRABECULAR MESHWORK
 Sieve like structure through which aqueous
humor leaves the eye.
 It converts the scleral sulcus into a circular
channel, called the Schlemm canal.
 Allows the bulk flow aqueous out of the
anterior chamber but prevents blood reflux
into anterior chamber.

38.  Hence, forms the crucial part of normal blood-
aqueous barrier
 Fibronectin, elastin, laminin, collagen (types I,
III, IV, V and VI), smooth muscle myosin
containing cell are the integral components of
trabecular meshwork.

39. It is divided into three
portions:
1. Uveal Meshwork
2. Corneoscleral
Meshwork
3. Juxtacanalicular
Meshwork

40. UVEAL MESHWORK
 Innermost part, extended from iris root and
ciliary body to Schlemm’s Canal
 The trabeculae of uveal meshwork are cord like
and 2 to 3 layers thick containing irregular
openings varying in size from 25μ to 75μ.

41. CORNEO-SCLERAL
MESHWORK
 Larger middle portion extending from scleral
spur to lateral wall of scleral sulcus
 Consists of flat sheets of trabeculae with
elliptical openings ranging from 5μ to 50μ

42. JUXTA-CANALICULAR
MESHWORK
 Outermost portion of trabecular meshwork
 It mainly offers resistance to normal aqueous
outflow
 This narrow part of trabeculum connects
corneoscleral meshwork with Schlemm’s Canal.

43. SCHLEMM’S CANAL
 Endothelial lined oval channel present
circumferentially in the scleral sulcus
 Cells of inner wall are irregular, spindle
shaped and contains giant vacuoles
 Cells of outer wall are smooth and flat
containing numerous opening of collector
channels.

44. COLLECTOR CHANNELS
 Also called
Intrascleral Aqueous
Vessels
 25 to 35 in number
 Leave Schlemm’s
Canal at oblique
angles to terminate
ultimately into

45. EPISCLERAL VEINS
Drains ultimately into cavernous sinus via
anterior ciliary and superior ophthalmic veins.

46. AQUEOUS HUMOR
OUTFLOW
 Conventional or trabecular outflow
(90% of the aqueous outflow)
 Unconventional or uveoscleral outflow
(10% of the aqueous outflow)

47. CONVENTIONAL OR
TRABECULAR OUTFLOW
 The aqueous humor leaves the eye at the
anterior chamber angle through trabecular
meshwork, the Schlemm’s canal, intrascleral
channels, and episcleral and conjunctival veins.

48. UNCONVENTIONAL OR
UVEOSCLERAL OUTFLOW
 The aqueous humor exits through the root of
iris, between the ciliary muscle bundles, then
through the suprachoroidal – scleral tissues.
CLINICAL CORRELATION
Prostaglandins used to reduce IOP in various conditions including glaucoma
reduce IOP by
increasing the aqueous drainage via this pathway.

50. Ciliary Process
Posterior Chamber
Anterior Chamber
Ciliary Body
Suprachoroidal
Space
Venous circulation
of ciliary body,
sclera and orbit
Trabecular
Meshwork
Schlemm’s Canal
Collector Channels
Episcleral Veins
Uveoscleral
Outflow(10%)
Trabecular
Outflow(90%)

51. Different Mechanisms of Outflow
Obstruction
 POAG - loss of trabecular endothelial cells, collapse
of schlemms canal, obstruction of collector channels.
 Infantile glaucoma – outflow structures not developed
properly (Trabeculodysgenesis).
 Angle closure glaucoma – peripheral iris pushed
against meshwork.
 Secondary open angle – obstruction by fibrovascular
tissues, RBCs, WBCs, tumor cells, pigment & lens
particles.

52. PHARMACOLOGY
Pilocarpine:
Miotic induced
contraction of sphincter
pupillae -> pulls the
peripheral iris away from
the trabeculum -> opens
the angle.
Contraction of the cilairy
muscle-> traction on
trabecular meshwork ->
drains the aqueous.