mechanismsofangleclosureglaucoma-150821155430-lva1-app6891.pdf

mechanism

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/inuitsprevalence 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 pradesheye disease study –0.71%
•Chennai eye disease incidence study –1.58%

6. •Traditionally, the angle-closure glaucomasare
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,orepithelial downgrowthinitiates
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/anteriorlypositioned/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.Anticholinergicagents
ii.Adrenergic agents
c.Emotional stress

15. PUPILLARY BLOCK MECHANISM
•Pupillaryblock 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 pupillaryplane
modulates flow of aqeousfrom 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 pupillaryblock is present
when increased iris convexity brings
perpipheraliris into apposition with TM
•Iris bombe would be expected with pressure
differentials of 10-15 mmHg

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

21. •Plateau iris configuration refers to an
anteriorlydisplaced 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 gonioscopyreveals double hump
sign / sine wave sign
•UBM –anterior rotation of ciliaryprocesses
•LPI / Lens extraction does not change
iridociliaryapposition

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 mioticsand
improves with cycloplegicsas they tighten
the ciliarybody zonularring and move the
lens posteriorly

26. CILIOCHOROIDAL EXPANSION
SYNDROMES
•In eyes predisposed to angle closure by virtue
of their small dimensions , choroidalvolume
expansion could contribute to disease by
increasing resistance in iris lens channel
intensifying pupil block
•Seen in choroidalhemorrhage, metastatic
tumors, inflammation (uvealeffusion , VKH ,
Panretinalphotocoagulation) , Sturgeweber,
CCF , scleralbuckling

27. ANTERIOR ACG
•These pathologies cause initial synechialclosure
in contrast to most others decribedwhich cause
appostionalclosure first followed by synechial
closure
•Examples-closure by neovascularmembrane
proliferating endothelial membrane
(iridocornealendothelial syndrome), by
inflammatory KPs making contact with iris from
the TM (sarcoidosisand chronicuveitis), etc.