INTRODUCTION PRIMARY OCULAR STRUCTURES AQUEOUS OUTFLOW SYSTEM PRODUCTION OF AQOUEOUS HOUMOUR DRAINAGE MAINTAINENCE OF INTRAOCULAR PRESSURE

1. AQUEOUS HUMOUR
Presenter- Shayri Pillai
Liberia Eye Centre
JFK Memorial Medical Centre
LV Prasad Eye Institute
Liberia
1st October 2019

2. AQUEOUS HUMOUR
DYNAMICS

3. CONTENTS
INTRODUCTION
PRIMARY OCULAR STRUCTURES
AQUEOUS OUTFLOW SYSTEM
PRODUCTION OF AQOUEOUS HOUMOUR
DRAINAGE
MAINTAINENCE OF INTRAOCULAR PRESSURE

4. Aqueous Humour
 Clear watery fluid
 Filling the anterior chamber (0.25 ml) and posterior
chamber (0.06 ml) of the eyeball
 Refractive index of aqueous humour is 1.336

5. INTRODUCTION
 Produced in the posterior chamber and flows through
the pupil into the anterior chamber.
 Exits the eye by passing through the
 Trabecular meshwork
 Into Schlemm’s canal
 Draining into the venous system through a plexus of
collector channels
 As well as through the uveoscleral pathway

6. Functions :
Maintains a proper intraocular pressure
 It plays an important metabolic role by providing
substrates and by removing metabolites from the
avascular cornea and lens
It maintains optical transparency

7. Allows for optical clarity and reflects the integrity
of the blood-aqueous barrier of the normal eye
It takes the place of lymph that is absent within
the eyeball

8. Composition
 Water 99.9 and
 Solids 0.1% which include :
 Proteins (colloid content)
 Amino acid about 5 mg/kg water
 Non-colloid constituents in millimols /kg water are
glucose (6.0), urea (7), ascorbate (0.9), lactic acid
(7.4), inositol (0.1), Na+ (144), K+ (4.5), Cl— (10), and
HCO3— (34)

9.  Oxygen is present in aqueous in dissolved state
 High concentrations of ascorbate, pyruvate and
lactate
 Low concentration of protein, urea and glucose

10.  Aqeuous humour in AC differs from aqueous humour
in posterior chamber because of metabolic interchange
 HCO3— in posterior chamber aqueous is higher than
in the anterior chamber
 Cl— concentration in posterior chamber is lower than
in the anterior chamber
 Ascorbate concentration of posterior aqueous is
slightly higher than that of anterior chamber aqueous

11. Aqueous pathway and structures in the angle of the
anterior chamber
Sihota, R. et.al. Parson’s: Diseases of the Eye. 22nd Edition 2015. India. P-288

12. PRIMARY OCULAR STRUCTURES INVOLVED:
 CILIARY BODY
 ANGLE OF ANTERIOR CHAMBER
 AQUEOUS OUTFLOW SYSTEM

13. Ciliary Body
 Main site of aqueous production
 Shape of the ciliary body is like an isosceles triangle
with its base forwards
 Iris is attached to about the middle of the base of the
ciliary body
 Outer side of the triangle lies against the sclera with
the suprachoroidal space in between

14. Angle of Anterior Chamber
 Important role in the process of aqueous drainage
 Formed by the root of iris, anterior most part of the
ciliary body, scleral spur, trabecular meshwork and
Schwalbe’s line
 Angle width varies in different individuals
 Plays a vital role in the pathogenesis of different types
of glaucoma

15.  Internal scleral sulcus accommodates the Schlemm canal
externally and the trabecular meshwork internally
 Schwalbe line, the periphery of Descemet's membrane,
forms the anterior margin of the sulcus
 Scleral spur is its posterior landmark.

16. Section of the anterior ocular structures showing region
of the anterior chamber

17. Aqueous outflow system
Includes:
Trabecular meshwork
Schlemm’s canal
Collector channels
Aqueous veins
Episcleral veins

18.  The mean value reported ranges from 0.22 to 0.30
uL/min/mm Hg
 Outflow facility decreases with age and is affected by
surgery, trauma, medications, and endocrine factors
 Patients with glaucoma and elevated lOP have
decreased outflow facility

19. Mechanism of aqueous formation, flow and outflow
pathways in the normal eye

20.  Trabecular Meshwork
Composed of multiple layers
Each of which consists of a collagenous connective
tissue core covered by a continuous endothelial layer
covering
 It is the site of pressure-dependent outflow

21. The trabecular meshwork functions as a 1-way valve
Permits aqueous to leave the eye by bulk flow but
limits flow in the other direction
Independent of energy
Number of trabecular cells decreases with age and
the basement membrane beneath them thickens

22.  Sieve-like structure through which aqueous humour
leaves the eye
Scanning electron micrograph of the trabecular meshwork
Bowling , B. Kanski’s Clinical Ophthalmology: A Systemic Approach, 8th Ed., 2016.
Australia. P-306

23. Trabecular Meshwork consists of three portions:
 Uveal meshwork
 Corneoscleral meshwork
 Juxtacanalicular (endothelial) meshwork

24. Uveal meshwork
 Innermost part of trabecular meshwork
 Extends from the iris root and the ciliary body to the
peripheral cornea
 The arrangement of uveal trabecular bands create
openings of about 25 m to 75 m

25. Corneoscleral meshwork
 Forms the larger middle portion
 Extends from the scleral spur to the lateral wall of the
scleral sulcus
 Consists of sheets of trabeculae that are perforated
by elliptical openings which are smaller than those in
the uveal meshwork (5 µ-50 µ)

26. Juxtacanalicular (endothelial)
meshwork
Forms the outermost portion of meshwork
Consists of a layer of connective tissue lined on
either side by endothelium
 Narrow part of trabeculum connects the
corneoscleral meshwork with Schlemm’s canal
This part of trabecular meshwork mainly offers the
normal resistance to aqueous outflow

27.  Schlemm’s canal
 An endothelial lined oval channel present
circumferentially in the scleral sulcus
 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

28. Collector channels
Also called intrascleral aqueous vessels, are about
25-35 in number
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

29.  Larger vessels (aqueous veins) run a short
intrascleral course and terminate directly into
episcleral veins (direct system)
Smaller collector channels form an intrascleral
plexus before eventually going into episcleral veins
(indirect system)

30. Semidiagrammatic representation of the structures of the angle of the anterior
chamber and ciliary body.
Skuta,G.L. et.Al. American Academy of Ophthalmology Fundamental basics 2016 Edition.USA P.-51

31. PHYSIOLOGY

32.  The physiological processes concerned with the
dynamics of aqueous humour are:
 Production
 Drainage
 Maintenance of intraocular pressure

33. Production
 Aqueous humour is derived from plasma within the
capillary network of ciliary processes.
 The normal aqueous production rate is 2.3 µl/min.
 The three mechanisms ultrafiltration, secretion
(active transport) and diffusion play a part in its
production at different levels.

34. Ultrafiltration
Most of the plasma substances pass out from the
capillary wall, loose connective tissue and pigment
epithelium of the ciliary processes
 Plasma filtrate accumulates behind the non pigment
epithelium of ciliary processes
Ultrafiltration refers to a pressure-dependent
movement along a pressure gradient

35. Secretion
 Tight junctions between the cells of the non-
pigment epithelium create part of blood aqueous
barrier
 Certain substances are actively transported
(secreted) across this barrier into the posterior
chamber
 Active transport is brought about by Na+-K+
activated ATPase pump and Carbonic anhydrase
enzyme system.
 Substances that are actively transported include
sodium, chlorides, potassium, ascorbic acid,
amino acids and bicarbonates

36.  Active secretion, or transport consumes energy to
move substances against an electrochemical gradient
and is independent of pressure.
 Active secretion accounts for the majority of aqueous
production and involves, at least in part, activity of the
enzyme carbonic anhydrase II.

37. Diffusion
Active transport of these substances across the non-
pigmented ciliary epithelium results in an osmotic
gradient
Movement of other plasma constituents into the
posterior chamber by ultrafiltration and diffusion
Sodium is primarily responsible for the movement of
water into the posterior chamber

38.  Diffusion is the passive movement of ions across a
membrane related to charge and concentration
 Ultrafiltration and diffusion, the passive mechanisms
of aqueous formation, are dependent on the level of
blood pressure in the ciliary capillaries, the plasma
osmotic pressure and the level of intraocular pressure

39. The rate of aqueous formation is affected by a variety of
factors:
 Integrity of the blood-aqueous barrier blood flow to the
ciliary body
 Aqueous humor production may decrease following
trauma or intraocular inflammation and following the
administration of certain drugs
 Carotid occlusive disease may also decrease aqueous
humor production.

40. Drainage
Aqueous humour flows from the posterior chamber
into the anterior chamber through the pupil against
slight physiologic resistance
From the anterior chamber the aqueous is drained
out by two routes:
 Trabecular (conventional) outflow
 Uveoscleral (unconventional) outflow

41. Trabecular (conventional) outflow
Trabecular meshwork is the main outlet for aqueous
from the anterior chamber
Approximately 90 percent of the total aqueous is drained
out via this route
Free flow of aqueous occurs from trabecular meshwork
up to inner wall of Schlemm's canal which appears to
provide some resistance to outflow

42. Mechanism of aqueous transport across inner wall of
Schlemm’s canal:
 According to vacuolation theory, transcellular spaces exist
in the endothelial cells forming inner wall of Schlemm's
canal
 These open as a system of vacuoles and pores, primarily
in response to pressure
 Transport the aqueous from the juxtacanalicular
connective tissue to Schlemm’s canal

43.  A pressure gradient between intraocular pressure and
intrascleral venous pressure (about 10 mm of Hg) is
responsible for unidirectional flow of aqueous

44. Vacuolation theory of aqueous transport across the inner wall of the Schlemm's
canal

45. Uveoscleral (unconventional) outflow
Responsible for about 10 percent of the total aqueous
outflow
Aqueous passes across the ciliary body into the
suprachoroidal space
Drained by the venous circulation in the ciliary body,
choroid and sclera

46.  In the normal eye, any nontrabecular outflow is termed
uveoscleral outflow
 Uveoscleral outflow is also termed pressure-
independent outflow
 It can be influenced by the age
 It is increased by cycloplegia, adrenergic agents,
prostaglandin analogs, and certain complications of
surgery (eg, cyclodialysis) and is decreased by miotics

47. Flow chart depicting drainage of aqueous humour

48. Maintenance of intraocular pressure
 The intraocular pressure (IOP) refers to the pressure
exerted by intraocular fluids on the coats of the
eyeball
 The normal IOP varies between 10 and 21 mm of Hg
(mean 16 ± 2.5 mm of Hg)
 The normal level of IOP is essentially maintained by
a dynamic equilibrium between the formation and
outflow of the aqueous humour

49. The most important factor which causes rise of
intraocular pressure is obstruction to the drainage of
the aqueous humor through the:
 Angle of the anterior chamber
 At the pupil

50.  Various factors influencing intraocular pressure can
be grouped as under:
 Local factors
Rate of aqueous formation influences IOP levels
The aqueous formation in turn depends upon many
factors such as permeability of ciliary capillaries and
osmotic pressure of the blood

51. Resistance to aqueous outflow (drainage).Most of the
resistance to aqueous outflow is at the level of trabecular
meshwork
 Increased episcleral venous pressure may result in rise
of IOP
Dilatation of pupil in patients with narrow anterior
chamber angle may cause rise of IOP owing to a
relative obstruction of the aqueous drainage by the iris

52. General factors
 Heredity- It influences IOP, possibly by multifactorial
modes
 Age- The mean IOP increases after the age of 40
years, possibly due to reduced facility of aqueous
outflow
 Sex- IOP is equal between the sexes in ages 2040
years. In older age groups increase in mean IOP
with age is greater in females

53.  Diurnal variation of IOP- Usually, there is a tendency of
higher IOP in the morning and lower in the evening
 Postural variations-IOP increases when changing from
the sitting to the supine position
 Blood pressure-Prevalence of glaucoma is marginally
more in hypertensives than the normotensives

54.  General anaesthetics and many other drugs also
influence IOP e.g., alcohol lowers IOP, tobacco
smoking, caffeine and steroids may cause rise in IOP
 In addition there are many anti-glaucoma drugs which
lower IOP.

55. Thank you!
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