ACG

1. MECHANISMS OF
ANGLE CLOSURE
GLAUCOMA

4. • Of the estimated 67 million people
worldwide thought to have glaucoma one
third to one half have PACG
• In Europeans and Africans POAG is five times
more common than PACG
• In Chinese, Mongolians, Indians frequency of
PACG may be equal to or greater than POAG
• In Eskimos/inuits prevalence of PACG higher
than any other group
• PACG is 2-3 times more likely to be visually
disabling than POAG

5. • Data from India
• Vellore eye study – 4.32%
• Andhra pradesh eye disease study – 0.71%
• Chennai eye disease incidence study – 1.58%

6. • Traditionally, the angle-closure glaucomas are
separated into 2 main categories: primary
and secondary angle closure.
• In primary angle closure, there is no
underlying pathology; there is only an
anatomic predisposition.
• In secondary angle closure, an underlying
pathologic cause, such as an intumescent
lens, iris neovascularization, chronic
inflammation, corneal endothelial
migration,or epithelial downgrowth initiates
the angle closure

12. Risk Factors
1. Demographic factors:
a. Age (> 60 years old)
b. Female sex
c. Chinese ethnic origin
d. Family history (especially first-degree
relatives, because ocular anatomic features
are inherited)

13. 2. Anatomic factors:
a. Shallow anterior chamber depth,
especially peripherally ( Mean -1.8mm)
b. Thick/anteriorly positioned/increased
anterior curvature of
lens (0.35mm/0.65mm)
c. Short axial length
d. Small diameter/increased curvature of
cornea
e. Plateau iris configuration/thick peripheral
iris roll

14. • 3. Precipitating factors:
a. Dim illumination (including extremes of
temperature causing people to stay indoors)
b. Drugs
i. Anticholinergic agents
ii. Adrenergic agents
c. Emotional stress

15. PUPILLARY BLOCK MECHANISM
• Pupillary block is the fundamental
mechanism underlying the spectrum of PAC
• Involves – lens iris apposition at the pupil
with resultant bowing forward of peripheral
iris as aqueous pressure builds up in
posterior chamber
• An anatomically predisposed eye that allows
anterior displaced peripheral iris to block TM
as

16. • Junction of lens and iris at pupillary plane
modulates flow of aqeous from posterior to
anterior chamber – Iris lens channel
• Functions as a relative one way valve to
sustain a minimally high pressure(0.23mm
Hg) in the posterior chamber than in the
anterior chamber hence directing anterior
flow forward
• Pupil block is a relative resistance that is
present in most eyes

18. Whether this leads to angle closure or not
depends upon:
1)baseline position of iris
2)iris stiffness
3)size of pressure differential
4)iris lens channel resistance
Clinically significant pupillary block is present
when increased iris convexity brings
perpipheral iris into apposition with TM
• Iris bombe would be expected with pressure
differentials of 10-15 mmHg

20. PLATEAU IRIS
• Barkan noticed that 20% of eyes with ACG
were atypical as they had normal central ACD
no iris bombe and minimal pupillary block
• Schaffer and Chandler – plateau iris
• Wand – two entities - plateau iris
configuration and plateau iris syndrome

21. • Plateau iris configuration refers to an
anteriorly displaced peripheral iris
compromising the angle
• Plateau iris syndrome refers to angle closure
either spontaneously or after
pharmacological dilatation in an eye with a
patent iridotomy
• Pseudo plateau iris syndrome – iridocliary
cyst pushing the iris from behind

23. • Depending on the amount of obstruction that
develops acute or chronic angle closure can
occur
• Indentation gonioscopy reveals double hump
sign / sine wave sign
• UBM – anterior rotation of ciliary processes
• LPI / Lens extraction does not change
iridociliary apposition

24. LOSS OF IRIS VOLUME
• There is remarkable loss of iris area(10%) and
volume(4%) with pupil dilatation most
probably by exchange of extracellular fliud
with aqueous
• Quigley et al proved that eyes with ACG
retained more iris volume with pupil
dilatation than controls – a feature that made
angle closure more likely

25. LENS INDUCED ACG
• In this form lens moves forward excessively
pushing the iris forward into anterior
chamber
• This subset worsens with miotics and
improves with cycloplegics as they tighten
the ciliary body zonular ring and move the
lens posteriorly

26. CILIOCHOROIDAL EXPANSION
SYNDROMES
• In eyes predisposed to angle closure by virtue
of their small dimensions , choroidal volume
expansion could contribute to disease by
increasing resistance in iris lens channel
intensifying pupil block
• Seen in choroidal hemorrhage , metastatic
tumors , inflammation (uveal effusion , VKH ,
Panretinal photocoagulation) , Sturge weber ,
CCF , scleral buckling

27. ANTERIOR ACG
• These pathologies cause initial synechial closure
in contrast to most others decribed which cause
appostional closure first followed by synechial
closure
• Examples- closure by neovascular membrane
proliferating endothelial membrane
(iridocorneal endothelial syndrome), by
inflammatory KPs making contact with iris from
the TM (sarcoidosis and chronicuveitis), etc.