Download Fundamental Concepts of Chronic Angle

Prin Rojanapongpun
Journal of Current Glaucoma
Practice, May-August 2007;1(1):42-46
Fundamental Concepts of
Chronic Angle-closure Glaucoma
Prin Rojanapongpun
Chulalongkorn University & Hospital, Bangkok, Thailand
e-mail: [email protected]
INTRODUCTION
Chronic angle-closure glaucoma (CACG) is often asymptomatic.
Many patients are diagnosed as chronic open-angle glaucoma
(COAG) until accurate gonioscopy is performed. CACG is the
most common form of angle-closure glaucoma (ACG) seen in
the clinic,1 as well as in population-based surveys.2-5 This article
describes diagnostic and therapeutic concepts of CACG.
CLINICAL CHARACTERISTICS AND SUBTYPES OF
CHRONIC ANGLE-CLOSURE GLAUCOMA
Clinical Characteristics
CACG is composed of two clinical entities: angle-closure and
glaucomatous optic neuropathy (GON) with functional and
structural changes. Angle-closure, which is a mechanical
blockage of the trabecular meshwork, precedes the development
of glaucomatous optic neuropathy.
The onset of CACG is generally gradual but could be a
consequence of an acute episode of angle-closure (AAC). In
another word, CACG could develop after one or several AAC
attacks, or gradually develop from appositional closure or
creeping angle. The clinical presentation includes signs and
symptoms of optic neuropathy and angle-closure.
Subtypes of CACG
angle. Even in area without PAS, there was evidence of loss of
endothelial cells and reactive repair processes.6 Based on a
clinic-based study,7 patients with asymptomatic CACG were
older than patients in the symptomatic group, were more often
men, more likely to have either diabetes mellitus or hypertension.
Symptomatic CACG
Symptomatic CACG develops after AAC or intermittent angleclosure attack. Patient has variable degree of pain and headache,
from very mild and vague aching pain to classic signs and
symptoms of AAC. The visual symptoms like halo and blurred
vision can be quite variable as well. On slit lamp examination,
the ocular sign of ischemic sequel of AAC is usually seen in the
anterior segment including distortion of iris tissue (iris whirling),
necrosis of subcapsular lens epithelium (glaukomflecken), and
pupillary distortion and dilatation. There is also a significant
decrease in the corneal endothelial cell density in CACG eyes
that have had AAC attack, which is more pronounced than
those with intermittent attack.6 Delay in presentation (>24 hours)
and unresponsiveness to medical treatment in termination of
the acute attack in an acute angle-closure glaucoma patient had
been identified as a significant risk in developing CACG.8
Symptomatic CACG eyes were more hypermetropic and had
more iridocorneal synechiae and large areas where the pupillary
ruff was absent.7
Based on symptoms, CACG can be categorized into two main
subtypes, asymptomatic and symptomatic CACG.
PATHOGENESIS AND NATURAL HISTORY OF CACG
Asymptomatic CACG
Eyes with relatively smaller anterior segment are prone to
develop angle-closure. Eyes with chronic angle-closure
glaucoma have different anterior segment anatomical
relationships when compared to normals.9,10 The eye at risk
tends to be hypermetropic with a shallow anterior chamber, a
relatively anteriorly positioned lens and a short axial length.11
East or Southeast Asian ethnic background is an important risk
factor for the development of chronic angle-closure glaucoma.
Other demographical risk factors include older age, female gender
and a familial tendency.4,12-16 Both increasing age and female
Asymptomatic CACG is a more common subtype. The sign and
symptom are similar to open-angle glaucoma except findings
associated with angle-closure. The patient has no symptom of
pain nor headache or history of acute attack. The eye gradually
develops angle-closure from appositional closure to synechial
closure, so called ‘creeping’ angle-closure. However, iridotrabecular contact slowly increases in circumference and height
leading to compromised outflow and raised IOP. Prolonged
contact leads to PAS as well as acquisition of pigment at the
Risk Factors of Angle-closure
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Fundamental Concepts of Chronic Angle-closure Glaucoma
gender are known to have shallower anterior chamber which
predispose angle-closure. Such association is observed in all
races.17 Shallow anterior chambers are a significant risk factor
for angle-closure in East Asians, although the nature of the
association is specific to the individual population.18 There is
still a controversy why East Asians have more prevalence of
ACG as some known biometric risk factors are not different to
other ethnic groups.19 A clinic-based study comparing the angle
width of Asians, Afro-Americans, and Caucasians,
demonstrated no statistically significant difference between the
three groups. But the iris joins the scleral wall more anteriorly in
Asians, slightly more posteriorly in Afro-Americans, and most
posteriorly in Caucasians. Thicker lens, anteriorly positioned
of the lens20 and smaller corneal diameter are also identified as
risk factors.21-23 The role of the ciliary body anatomy and ciliary
processes in the pathogenesis of this condition requires further
investigation. Uptodates, there is no exact gene identified
specifically for ACG.24
Fig. 1: Angle-closure glaucoma cascade
Mechanisms of Angle-closure
There are several angle-closure mechanisms that play part in
causing anatomical angle-closure. These include pupillary block,
plateau iris, thick peripheral lens, lens-related causes, and ciliary
block. Classification of mechanism into four level of blockage
identifies obstructions to aqueous flow at different levels is
widely accepted and practical.25
Pupillary block is the most common mechanism and presents
in almost every case, other mechanism must also be identified.
This leads to the common clinical observation and the use of
terminology like ‘residual’ glaucoma, or so called ‘postiridectomy’ glaucoma, was commonly used in the past for ACG
after successful iridectomy.26 The terminology signifies that
other mechanisms, in addition to pupillary block, probably coexist in the angle-closure eye. A rather comprehensive study
using biometry, UBM and gonioscopy, demonstrated that
approximately half of the CACG eyes may have multiple
mechanisms contributing to the closure of drainage angle.27
Angle-closure Glaucoma Cascade
Angle-closure glaucoma can be viewed as a cascade of events
(Fig. 1). The initial stage or the beginning of the cascade are the
eyes that have relative anatomical abnormalities predisposing
to the development of angle-closure and proceeding on to the
final and common stage of glaucomatous neuropathy.
Based on International Society of Geographical
Epidemiological Organization (ISGEO) classification, the term
‘angle-closure suspect (ACS)’ is suggested for the initial stage.
This is similar to ‘occludable’ angle that is commonly used in
the clinic. ‘Occludable’ describes eye that the angle is closeable
or the trabecular meshwork become non-visible but with normal
IOP, disk and field. Clinicians sometimes use the term of ‘narrow’
43
angle interchangeably with ‘occludable’, though these two terms
are not similar. The term “narrow” also reflects what clinician
actually sees with slit lamp biomicroscopy and gonioscopy.
Lots of debates have been going on to determine which
terminology best reflects the condition. Recently, the
Association of International Glaucoma Society (AIGS)
suggested that ‘anatomical narrow angle (ANA)’ may be more
appropriate as it represents the actual findings. The term ‘ANA’
emphasizes that the angle inlet is narrow as identified on
gonioscopy and is likely to close under certain condition. If
these eyes are treated early enough, angle-closure will not occur,
thus preventing the cascade of angle-closure events. In another
word, if angle-closure mechanism(s) can be corrected in time,
most eyes return to normal.
If ACS is not treated early enough, it may develop into the
next stage of angle-closure. The drainage angle is then closed
with or without PAS. The mechanism of angle-closure could be
single or multiple. As a result, IOP raises either acutely or
chronically leading to the next stage coined ‘angle-closure (AC)’.
At this stage, even if the angle-closure mechanism is corrected,
IOP is still high. The magnitude of IOP rise depends on outflow
reserve and degree of trabecular damage. The underlying angleclosure mechanism must be identified and corrected.
If treatment fails to prevent further and long-standing IOP
rise, the eye progress to the final stage of the cascade. This is
when glaucomatous optic neuropathy is evidenced, usually
with detectable functional defect. The stage is ‘angle-closure
glaucoma (ACG)’ when both angle-closure and glaucomatous
optic neuropathy are present together. Clinically, the eye is
diagnosed as CACG.
Prin Rojanapongpun
Clinical Significance of Different Disease Stage
Differentiating angle-closure into different stages does have
clinical significance. Each stage indicates the presence or
absence of the different end organ damage, which implies
severity and chronicity of the condition, leads to better
understandings of the treatment outcome. For example, the
efficacy of LPI in prevention of IOP rise depends on the stage
of angle-closure. In primary angle-closure suspect (PACS), a
prophylactic LPI prevent further IOP rise in 97 percent based
on a population-based study in an East Asian population.28
Another study29 showed that LPI successfully prevented
further IOP rise in 89 percent of fellow eyes (in patients with
acute attack) without the need for additional glaucoma treatment
in the long-term. These fellow eyes could be viewed as good
representatives of the high risk angle-closure suspect (ACS)
eyes. Another retrospective study30 demonstrated that once
the eye already had acute angle-closure attack, only 41.8 percent
were successfully treated with LPI alone while the rest developed
IOP rise that requiring further treatment at a mean follow-up of
50.3 months. However, in eyes with established glaucomatous
optic neuropathy at diagnosis (ACG eyes), despite the presence
of a patent LPI, most eyes require further treatment to control
IOP. In a retrospective review of 83 ACG eyes, only five eyes
(6%) did not require any treatment after LPI in the long-term.31
So LPI is very effective in preventing angle-closure if it is
performed early enough at the ACS stage. But if ACS already
turns into AC stage, LPI alone become less effective and not
optimal. However, when glaucomatous optic neuropathy is
evidenced, LPI is not effective in treating or preventing further
IOP rise. Majority of such eyes fail to have IOP control without
medication or filtering surgery.11 Whether there are other
mechanisms of angle-closure that cannot corrected with LPI or
extensive damage has already occurred at the drain are to be
investigated in each individual. The essence is that staging of
angle-closure is important to the treatment approach and
outcome determination.
TREATMENT CONCEPTS
Basic Principles
There are three basic principles of treatment in CACG. First,
remove angle-closure by modification and correction of the
angle-closure mechanism(s). Second, control the IOP and other
associated risk factors. And third, monitor and maintain the
structural and functional integrity of the optic disk and the
retinal nerve fiber layer similar to treating other type of
glaucomatous optic neuropathy.
Management Steps of CACG
There are five steps in the management of CACG (Table 1). The
first step is to document the angle-closure and glaucoma by
Table 1: Steps in the management of chronic
angle-closure glaucoma
1. Document angle-closure and glaucoma (presence or evidence of
peripheral anterior synechiae, previous angle-closure attack,
intraocular pressure rise, glaucomatous disk change, visual function
change)
2. Identify and correct angle-closure mechanisms
3. Medication and laser peripheral iridotomy
4. Reassessment after laser peripheral iridotomy for requirement for
iridoplasty, medications, or surgical intervention
5. Monitor intraocular pressure, optic disk, and visual field and
perform periodic gonioscopy
examination of the angle structures, including the trabecular
meshwork, and the extent of the angle-closure by slit-lamp
examination or gonioscopy. Indentation gonioscopy will help
to determine the presence of PAS. UBM provides a high
resolution image of the anterior segment structures and their
relationships. UBM is currently the best imaging technique to
view the posterior chamber and ciliary body, surpassing
gonioscopy for dynamic study of the angle and revealing more
information such as occludable angles.
The second step is to identify and correct the angle-closure
mechanism. Pupillary block is the most common mechanism
and is easily corrected by laser peripheral iridotomy (LPI) to
open the angle. However, other mechanisms also need to be
identified. As discussed earlier in this chapter, LPI is very
effective for preventing increased IOP in eyes with occludable
angles and ACS but is less effective for eyes with AAC and
those with GON.
The third step is performing LPI and use of medication to
control IOP. Medical therapy has recently become more
important for CACG as the IOP may remain high even after
successful iridotomy and iridoplasty. The efficacy of
prostaglandin in CACG therapy was proven in a large-scale
randomized multi-center study. The IOP reduction was 30 to 33
percent for eyes receiving latanoprost, compared with 20 percent
for eyes receiving timolol.32
This is followed by the next step of reassessment and further
treatment. Even after successful LPI, most patients with CACG
require further treatment, either because of multiple mechanisms
of angle-closure or because the angle structure has been
damaged to some extent. Patients therefore need to be
reassessed after LPI for further treatment in the form of
iridoplasty, medication, or surgery. Iridoplasty is effective for
AAC, but has no proven efficacy for CACG. However, there is
evidence to suggest that it is highly effective for pure plateau
iris syndrome in Caucasians.33
The final step in the management of CACG is to monitor
IOP, optic disk, and visual fields, and to perform periodic
gonioscopy. Glaucoma surgery by trabeculectomy remains the
next step for IOP control. However, the success is highly
44
Fundamental Concepts of Chronic Angle-closure Glaucoma
dependent on postoperative care and management, and the
outcome is variable.
SUMMARY
Fundamental concepts of CACG are important and must be
understood well by clinician to successfully diagnosis, treating
and assessing the outcome of CACG. The angle-closure
glaucoma cascade, mechanism of angle-closure, and risk factors
are described. Appropriate approach must be made by
identifying angle-closure mechanisms and stage of the disease.
The treatment concept is also outlined. LPI remains an important
step in treatment, but most eyes with CACG need further
treatment to control IOP, which relies largely on medication.
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