anatomy of aqueous humor , which maintains the pressure in the eye

1. AQUEOUS HUMOR
Dr.M.Sudheer Kumar
Ophthalmology post Graduate
Guntur Medical College

2. AQUEOUS HUMOUR
• The word aqueous derived from latin word aqua –
meaning water
• Aqueous humor is a transparent ,watery fluid similar
to plasma, but containing low protein concentration
• serves as a blood substitute for the avascular cornea,
lens,anterior vitreous and also the trabecular
meshwork (TM) of the outflow pathway.
• supplies nutrients and oxygen to these avascular
tissues through diffusion and also removes
metabolic wastes of the avascular tissues through its
continuous formation

3. ANATOMY:
• Ocular structures concerned with aqueous
humor
1. Ciliary body
2. Posterior chamber
3. Anterior chamber
4. Angle of anterior chamber
5. Aqueous out flow system

5. • Ciliary process (whitish finger like projections
70 to 80 in number) from the parsplicata
,part of ciliary body are site of aqueous
production.

6. • Each capillary consists of endothelium with
fenestrations
• Which is lined by basement membrane
• Pericytes are present in the basement
membrane
• Two layers of epithelium
• Inner non pigmented epithelium : the tight
junctions between the cells of this layer create
part of blood aqueous barrier.
• Outer pigmented epithelium contains melanin
granules.

7. 2.Posterior chamber:
• It is a triangular space between lens its
zonules - iris and part of ciliary body
• Freshly formed aqueous is poured into this
space
• Contains0.06ml of aqueous

8. • Posterior chamber is divided in to 3
compartments
a. Pre zonular space
b. Zonular space
c. Retro zonular space
a.Pre zonular space between posterior
surface of iris and anterior surface of
zonular fibres

10. b. zonular space /circumlental /cilio lental
space bounded
centrally - equator of lens
peripherally - ciliary process
anteriorly - posterior surface of anterior
zonular fibres
posteriorly - anerior surface of the
posterior zonular fibres
c.Retrozonular space between posterior
surface of zonules and peripheral part of
anterior vitreous .

11. 3.Anterior chamber:
anteriorly – Back of the cornea
posteriorly – Anterior surface of iris and
ciliary body
• It is about 3mm deep
• Contains 0.25 ml of aqueous
• Through pupil it communicates with pc
• Its peripheral recess is called angle of ac.
which is mainly formed by trabecular meshwork

12. 4. Angle of anterior chamber:
• Clinically angle of AC visualised by
gonioscopic examination
• From anterior to posterior it is formed by
following structures
a. Schwalbe’s line
b. Trabecular meshwork
c . Scleral spur
d. Ciliary band

13. a.schwalbe’s line
• Its formed by prominent end of the
descement’s membrane of cornea.
• contains circularly arranged collagen fibres
intermixed with elastic fibres.
• It marks the anterior limit of structures forming
the angle of anterior chamber .

14. b.Trabecular meshwork
• Its seen as a band just anterior to scleral spur
and covers the internal aspect of the canal of
Schlemm
• Appearance varies from faint tan to dark
brown on gonioscopy.
• The canal may sometimes be made visible
during gonioscopy, when blood refluxes
retrogradely into the canal, and appears as a
pink strip visible through the meshwork.
(Usually the canal is free of blood)

15. • reflux occurs because the gonioscope,
when applied to the surface of the eye,
obstructs episcleral venous drainage and
reverses blood flow
•

16. c.scleral spur
• its posterior portion of scleral sulcus
appear as prominent white line on gonioscopy.
•Recently it has been shown that there are
contractile, myofibroblast-Iike cells oriented
circumfercntially within the scleral spur, which
have sparse mitochondria and are rich in
smooth muscle alpha actin and myosin
•k/a scleral spur cells (SSC)
•changes in modulate outflow resistance by
alterinSSC tone might g trabecular architecture.

17. D. Ciliary band
• Its is formed by anterior most part of
ciliary body between its attachment to
scleral spur & insertion of iris
• In gonioscopic examination it appears
as dark brown band.

23. THE OUTFLOW APPARATUS
The features of the outflow apparatus are
as follows:
1. internal scleral sulcus
(a) sulcus
(b) Schwalbe's ring
(c) scleral spur
2. trabecular meshwork
(a) uveal meshwork
(b) corneoscleral meshwork
(c) trabecular structure
(d) iris processes
(e) pericanalicular connectivetissue
(f) extracellular matrix

24. • 3. canal of Schlemm and collector
channels
(a) Schlemm's canal
(b) endothelial lining
(c) giant vacuoles
(d) collector channels
4. intra scleral arteries of the limbus
5. innervation of the outflow apparatus
6. uveoscleral drainage pathway
7. location of the resistance to outflow

26. The sulcus
• The sulcus is a circular groove on the
inner aspect of the corneosclerallimbus
• extending from the termination of
Descemet's membrane, anteriorly
demarcated by Schwalbe's ring ,post
by the scleral spur.

27. • The sulcus completely accommodates
the canal of Schlemm externally and
corneo-scleral portion of the trabecular
meshwork internally.

28. TRABECULAR MESHWORK
• The trabecular meshwork is a
spongework of connective tissue
beams which are arranged as
superimposed perforated sheets.
• The inner portion of the trabecular
meshwork is referred to as the uveal
meshwork and the outer portion,
connected to the spur and closer to
Schlemm's canal, is the corneoscleral
meshwork.

29. • The meridional width of the trabecular
meshwork posteriorly, near the scleral
spur is 120-180 micro m.
• The dimensions are wider in the
myopic than the hypermetropic eye.
• Between the outermost corneoscleral
trabecular sheet and the endothelial
lining of Schlemm's canal is a cell rich
zone, the peri or juxta canalicular
connective tissue zone k/a endothelial
or cribriform mesh work

30. i. Uveal meshwork
• Innermost part of TM
• It extends from iris root and ciliary body,
to schwalbes line
• uveal meshwork (1- 2 layers) is made up
of cord-like trabeculae which interlace,
and taper anteriorly.
• The arrangement of uveal trabecular
bands create opening of 25 to 75 μ -least
resistance

31. ii. Corneoscleral meshwork
• larger middle portion
• Made up of flattened,perforated sheets
• Extends from scleral spur to lateral wall
of scleral sulcus .
• opening 5 to 50 μ
• Moderate resistance to flow

32. Trabecular structure
• The basic structure of the uveal and
corneoscleral sheet has a covering of
trabecular cells.
• trabecular cells are elongated in the long
axis of the trabecular sheet and are 4-8
micro m in thickness centrally, and about
120 micro m in length.
• The cells are actively phagocvtic and may
contain pigment and other inclusion
materials which increases with age.

33. • A number of authors believe that these
cells are involved in a self-cleaning
mechanism which keeps the trabecular
'filter' clean.
• These cells shows,nucleus, moderate
amount of mitochondria, rough and
smooth endoplasmic reticulum, well-
developed Golgi apparatus,
lysozomes, pinocytotic vesicles

35. Iris processes
• These are broad-based flat triangular
bands.
• Taper anteriorly and bridge the angle
recess from the iris root to the uveal
trabeculae into which they merge.
• They are usually sparse in number and
are found in about one-third of the normal
population
• Their structure resemblesthat of the iris
tissue with which they are continuous.

36. • Broad iris processes partially obscure the
angle recess.

37. Juxtacanalicular mesh work
• The peri or juxtacanalicular connective tissue zone
invests Schlemm's canal in its entire extent.
• Known as the endothelial meshwork or area
cribriforme.
• This region consists of 2 -5 layers of loosely arranged
cells embedded in an extracellular matrix
• The pericanalicular cells have important phagocytic
and secretory properties related to the self-cleaning
role of the meshwork
•

38. • and to the production of the extracellular
matrix,
• Juxta canalicular mesh work,make a
major contribution to outflow resistance.
• because the pathways are narrow and
tortuous, and also the presence of the
extracellular proteoglycans and
glycoproteins.

39. Extracellular matrix
• The pericanalicular region is
embedded in ECM
• ECM contains collagen types I, III , IV,
V,VI, fibronectin, chondroitin
,dermatan sulphates and hyaluronic
acid.
• open spaces in this region may contain
a gel-like substance which could
contribute to the resistance to aqueous
outflow.

40. Schlemm's canal
• The canal of Schlemm is a narrow circular
tube of 36 mm in circumference, which is
lined by endothelium.
• Lies in outer portion of the internal scleral
sulcus
• It conducts aqueous humour from the
trabecular region to the episcleral venous
network via the collector channels.
• pericanicular connective tissue scperate the
inner and outer walls of Schlemm's canal
from the trabecular meshwork and sclera,
respectively.

41. Giant vacuoles
• The most prominent features of the inner
wall of the Schlemm canal are the 'giant
vacuoles'.
• They arise by invagination of the basal
plasmalemma of the endothelial cells.
• smaller proportion of the vacuoles also
communicate with the canal of Schlemm via
a luminal opening, by whicha transcelluiar
channel may be formed.
• formation of endothelial vacuoles to be
pressure dependent

42. • So that their number and size are reduced at
low pressures and increased at high
pressures .

43. Collector channels
• The collector channels arise at irregular
intervals from the outer wall of the canal of
Schlemm.
• They are 25-35 in number and drain into three
interconnecting venous plexuses
1) deep scleral
2) mid scleral
3) episcleral venous plexuses.
• No valves are present in the system.

44. Direct system
• upto 8 of these vessels drain directly into the
episcleral venous plexus and are known as
aqueous veins.
• With the slit-lamp microscope,they may be
seen subconjunctivally either as clear
vessels, or showing a bilaminar flow pattern
repreSenting the presence of both blood and
aqueous.

45. • Indirect system
Finer collector channels
Inter connecting venous plexus
Deep intrascieralplexus
Mid intrascleral plexus
Episcleral venous plexus

46. • d.Episcleral veins
• Most of aqueous vessels drain into
episcleral veins
• The episcleral veins ultimately drain into
cavernous sinuses via anterior ciliary and
superior ophthalmic veins.
• The innervation of the outflow apparatus
derives from the supraciliary nerve plexus
and the ciliary plexus in the region of the
scleral spur.

47. UVEOSCLERAL DRAINAGE PATHWAY
• The anterior portion of the ciliary body
extends into the chamber angle and is
inverted internally by the uveoscleral
meshwork, behind the scleral spur.
• no continuous cellular layer on
the anterior iris face, so that aqueous has
direct access from the anterior chamber into
the ciliary body and then into the supraciliary
and suprachoroidal compartments.
• it accounts for about 10% of the total bulk
aqueous outflow in the human

50. • Three physiologic processes contribute
to the formation and chemical
composition of the aqueous humor:
– Diffusion
– Ultrafiltration
– Active secretion

51. Diffusion
• lipid-soluble substances are transported
through the lipid portions of the cell membrane
proportional to a concentration gradient across
the membrane.

52. Ultrafiltration
• water and water-soluble substances,limited by
size and charge, flow through the micropores
in the cell membrane in response to an
osmotic gradient or hydrostatic pressure;
• influenced by
intraocular pressure
blood pressure in the ciliary
capillaries
plasma oncotic pressure

53. Secretion
• Implies active transport that selectively
moves substance against its
electrochemical gradient across a cell
membrane.
• It is postulated that majority of aqueous
humor formation depends on active
transport.
• It is done by non-pigmented epithelial cells

54. • Diffusion and ultrafiltration are both passive
mechanisms
• with lipid- and water-soluble substances
from the capillary core traversing the stroma
and passing between pigmented epithelial
cells
• And limited by the tight junctions of the non-
pigmented epithelial cells.

55. LOCATION OF THE RESISTANCE TO
OUTFLOW
• vascular pressure in the episcleral venous
system is in the region of 9 mmHg and the
intraocular pressure varies between 10 and
21 mmHg.
• The pressure gradient from the anterior
chamber to the episcleral veins is explained
by a resistance to flow residing somewhere
in the conventional outflow pathway.
• The resistance has been calculated to be 3
mmHg/micro lit/min

56. • In primary open-angle glaucoma the
resistance to outflow
increases, due to changes in the
outflow structure

57. THE AGEING EYE AND OPEN-ANGLE
GLAUCOMA
• With ageing, the thickness of the trabecular
sheets increases two- to threefold, mainly
due to an accumulation of 'curly' collagen in
the cortical zone.
• Degenerative changes occur in the
trabecular cells and the number of cells is
reduced.
• subsequent fusion of the trabecular beams,
a process referred to as hyalinization of the
meshwork .

58. • Maintenance of iop :
• By virtue of this aqueous helps in
maintainig the shape and internal
arrangement of the eye
• Metabolic role:
• Cornea takes glucose and oxygen from
aqueous & releases lactic acid ,co2
,into the aqueous .
Functions of aqueous humor

59. • Lens : Uses oxygen glucose aminoacids and
potassium releases lactate ,sodium , pyruvate.
• Vitreous & retinal metabolism:
• Amino acids , & glucose pass into the vitreous from
aqueous .
Optical function
• The cornea aqueous interface acts as diverging
lens of low power
Clearing function
• Clears biood macrophages remnantsof lens matter
& products of inflammation from anterior chamber
of eye.

60. Clinical signifance of aqueous
• Glaucoma is a progressive optic neuropathy
where retinal ganglion cells and their axons die
causing a corresponding visual field defect.
• An important risk factor is increased intra ocular
pressure either through increased production or
decreased outflow of aqueous humour , thus
compromised blood supply to the optic nerve due
to mechanical compression exerted by
high IOP
• Increased resistance to outflow of aqueous
humour may occur due to an abnormal trabecular
mesh work or to obliteration of the meshwork due
to injury or disease of the iris

61. Aqueous misdirection
syndrome
• The pathogenesis of aqueous
misdirection is thought to involve
posterior misdirection of aqueous flow
by a relative pupillary block into or
behind the vitreous body; the
subsequent increase in vitreous
volume results in a shallower anterior
chamber and an increase in intraocular
pressure (IOP).

62. • LDH activity in the aqueous humour is
greatly elevated in retinoblastoma.
• Aqueous cells and flare: In case of
uveitis cells and flare can be seen
through the aqueous. These are the
protein particles leaked from the blood
ocular barrier.