Download Laser Iridotomy in the Angle-Closure Suspect

COVER STORY
Laser Iridotomy in the
Angle-Closure Suspect
When is this treatment warranted?
BY SHUCHI PATEL, MD
A
ngle-closure glaucoma (ACG) accounts for
10% of all glaucoma in the United States. This
form of the disease is more prevalent worldwide, however, with estimates that 5.3 million
people will be blinded by primary ACG by 2020.1
ACG is caused by apposition of the peripheral iris to
the trabecular meshwork, which reduces the drainage
of aqueous humor through the anterior chamber angle.
The principle cause of primary angle closure is pupillary block, whereas in secondary angle closure, there
is physical blocking of the angle. Treatment depends
on the type of angle closure present. Lowering IOP, if
elevated, is always the first priority. This step is usually
handled medically with topical therapy. If any degree
of pupillary block is present or a potential threat,
then a laser peripheral iridotomy (LPI) is indicated
(Figure 1). Understanding when an LPI is indicated
can help prevent delays in treatment as well as further
complications.
INDICATIONS FOR LPI
Acute Angle Closure
Ninety percent of all US patients presenting with
angle closure have pupillary block.2 Rapid reversal of
the block provides relief to the patient in addition
to minimizing the risk of vision loss and permanent
damage to the angle leading to chronically elevated
pressures. On examination, IOP is markedly elevated,
and the angle is closed on gonioscopy (Figure 2). Initial
therapy should be aimed at immediately lowering IOP
with topical or oral medication and clearing the cornea.
Osmotic agents such as glycerin used topically can aid
in clearing the cornea quickly. Once the physician is
able to visualize the iris, he or she should perform an
LPI to relieve the pupillary block, deepen the angle, and
lower the IOP. Relatively soon afterward, an LPI should
be performed on the contralateral eye. Without a prophylactic LPI, the risk of an acute attack in the fellow
eye may be as high as 51%.3
34 GLAUCOMA TODAY MARCH/APRIL 2015
A
B
Figure 1. A temporally placed LPI (A). Transillumination
confirms patency (B).
Occludable Angle
As mentioned earlier, any patient presenting with
angle closure should be treated by means of an LPI,
whereas a prophylactic LPI in individuals with a narrow
angle reduces the chance of pupillary block and subsequent acute angle closure. Patients may present with
symptoms of intermittent angle closure and complain
of occasionally blurred vision, pain, or redness, often
after the pupil dilated, such as in a dimly lit room. On
COVER STORY
A
“[In an eye with an occludable
angle,] if I can visualize less than
two quadrants of trabecular
meshwork, I proceed with an LPI.”
B
Figure 2. A narrow angle on gonioscopy with no angle
structures visible (A). An open angle with an easily visualized
scleral spur and ciliary body (B).
gonioscopy, the angle appears occludable, meaning that
the angle structures are not visible. There is no consensus
on the threshold of when to perform an LPI based on a
gonioscopic examination alone. Personally, if I can visualize less than two quadrants of trabecular meshwork, I
proceed with an LPI. In symptomatic patients or those in
whom indentation does not deepen the angle, an LPI is
also likely indicated.
Narrow Anterior Chamber Angle
Patients with a narrow angle may be asymptomatic,
but upon slit-lamp examination, the anterior chamber
may appear shallow. Furthermore, on gonioscopy, the
angle will appear narrow, and all angle structures likely
will not be visible. In these cases, it is often difficult to
determine if an LPI is necessary. An indication to proceed
with an LPI may be if the patient has risk factors such
as a family history of angle closure, an age over 60 years,
female gender, and hyperopia.4 In patients at increased
risk of angle closure, if an LPI is not implemented, a
gonioscopic examination should be performed prior to
any pupillary dilation to decrease the chance of inducing
angle closure.
Chronic Angle Closure
Often, patients with long-standing, intermittent angle
closure or narrow anterior chambers develop chronic
appositional closure of the angle. In these cases, peripheral anterior synechiae may be visible on gonioscopy.
The patient’s IOP will be elevated, but other signs of
acute angle closure such as corneal edema or pain will be
absent. In cases of chronic angle closure, an LPI relieves
any pupillary block, but the chronicity of apposition
means that the angle may not deepen due to synechiae
formation. Nevertheless, an LPI is essential to prevent
further pupillary block. Further laser or surgical intervention to reduce IOP may be needed.
Plateau Iris
Plateau iris is an anatomic variation in which the iris
root angles forward from its insertion point and then
again centrally.5 It is the only type of primary angle closure
without pupillary block. In eyes with a plateau iris configuration, an LPI is indicated to relieve any component
of pupillary block. The angle will often deepen after an
LPI in these patients. In contrast, those with plateau iris
syndrome will still have a narrow angle and increased pressure after an LPI. The procedure is still performed to make
the definitive diagnosis of plateau iris syndrome versus
configuration, but for the latter, further treatment such as
laser iridoplasty may be needed to open the angle.
Aqueous Misdirection
Patients with aqueous misdirection develop a shallow
anterior chamber due to the lens iris diaphragm’s being
pushed anteriorly by the trapped aqueous in the posterior chamber. This condition leads to a pupillary block
that can be relieved by an LPI. Additionally, further treatment for aqueous misdirection often involves disruption of the hyaloid face with an Nd:YAG laser, and the
presence of a peripheral iridotomy in phakic patients is a
prerequisite to be able to perform this procedure.
Pigment Dispersion Syndrome
The abnormal iris configuration in pigment dispersion syndrome leads to a reverse pupillary block. The iris
MARCH/APRIL 2015 GLAUCOMA TODAY 35
COVER STORY
Figure 3. Anterior segment optical coherence tomography measuring the angle of insertion and demonstrating a narrow
angle approach.
bows posteriorly, chafing the iris against the lens zonules
and releasing pigment that can block the trabecular
meshwork. An LPI may relieve the posteriorly bowed
iris configuration, decrease the release of pigment, and
prevent further progression of pigment dispersion
syndrome.
iridocorneal angle9,10 (Figure 3). Some studies have even
shown that, after pupillary dilation, the iris is measurably
thicker in patients with narrow angles, and AS-OCT may
be able to detect this change.11 After LPI, deepening of
the anterior chamber and angle is usually noted on slitlamp examination, gonioscopy, and even AS-OCT.
Secondary Angle Closures With Pupillary Block
Patients with secondary angle closure have an identifiable cause of iridocorneal apposition. Addressing
the underlying cause with procedures such as cataract
extraction offers definitive treatment but also carries
the risks involved with surgery. In such cases, an LPI performed prior to other surgical intervention can decrease
the risk of complications during surgery or relieve symptoms of acute angle closure and postpone the need for
surgery. Many secondary angle closures are lens induced.
Examples that may benefit from a therapeutic or prophylactic LPI are phacomorphic glaucoma, microspherophakia, and ectopia lentis.6-8
Uveitic eyes may also develop pupillary block secondary to fibrotic membranes or peripheral synechiae. The
pupil may be scarred to the anterior capsule, blocking
aqueous flow to the anterior chamber and leading to
an iris bombé formation. An LPI is indicated to restore
the proper flow of aqueous, deepen the chamber,
and decrease pressure. Caution is warranted, however, because the procedure may exacerbate ocular
inflammation.
CONTRAINDICATIONS
In secondary angle closure without pupillary block,
outflow is obstructed due to direct blockage of the trabecular meshwork, as in neovascular glaucoma and iridocorneal endothelial syndrome. An LPI is not indicated
in these cases. In drug-induced angle closure, treatment
is cessation of the causative agent; an LPI is not indicated.
ADDITIONAL TESTS TO DETERMINE LPI
CANDIDATES
When the chamber appears to be shallow but the
gonioscopic examination is inconclusive, other modalities or tests can aid diagnosis and treatment. Three different provocative tests have mostly fallen out of favor. A
modification I have used is to dilate the pupil with tropicamide alone and recheck the IOP 1 hour later. I consider an increase of more than 8 mm Hg from baseline to
be a positive test result and a risk factor for acute angle
closure. I strongly consider an LPI for these patients.
A more objective test is anterior segment optical
coherence tomography (AS-OCT). This technology can
measure anterior chamber depth and the degree of the
1. Quigley HA, Broman AT. The number of people with glaucoma worldwide in 2010 and 2020. Br J Ophthalmol.
2006;90(3):262-267.
2. Ritch R, Chang BM, Liebmann JM. Angle closure in younger patients. Ophthalmology. 2003;110:1880-1889.
3. Henrietta H, Chew P, Sng C, et al. A comparison of two approaches to managing acute primary angle closure in
Asian eyes. Clin Ophthalmol. 2013;7(7):1205-1210.
4. See JLS, Chew PTK. Angle-closure glaucoma. In: Yanoff M, Duker JS, eds. Ophthalmology. 3rd ed. Philadelphia,
PA; Mosby; 2009:1162.
5. Diniz F, Cronemberger S, Merula RV, Calixto N. Plateau iris. Arg Bras Oftalmol. 2008;71(5):752-758.
6. Kaplowitz K, Kapoor K. An evidence-based approach to phacomorphic glaucoma. J Clinic Exp Ophthalmol.
2012;S1:006. http://omicsonline.org/2155-9570/2155-9570-S1-006.digital/2155-9570-S1-006.html. Accessed
March 16, 2015.
7. Senthil S, Rao HL, Hoang NT, et al. Glaucoma in microspherophakia: presenting features and treatment
outcomes. J Glaucoma. 2014;23(4):262-267.
8. Tsilou E, MacDonald IM. Weill-Marchesani syndrome. In: Pagon RA, Adam MP, Bird TD, et al, eds. GeneReviews.
Seattle, WA: University of Washington, Seattle; 1993-2013.
9. Wong HT, Lim MC, Sakata LM, et al. High-definition optical coherence tomography imaging of the iridocorneal
angle of the eye. Arch Ophthalmol. 2009;127:256.
10. Guzman CP, Gong T, Nongpiur ME, et al. Anterior segment optical coherence tomography parameters in
subtypes of primary angle closure. Invest Ophthalmol Vis Sci. 2013;54:5281.
11. Quigley HA, Silver DM, Friedman DS, et al. Iris cross-sectional area decreases with pupil dilation and its dynamic
behavior is a risk factor in angle closure. J Glaucoma. 2009;18:173.
36 GLAUCOMA TODAY MARCH/APRIL 2015
CONCLUSION
An LPI is often indicated in patients with angle closure.
This procedure can treat pupillary block or prevent it
from occurring. Gonioscopy and knowledge of angle
anatomy are fundamental to identifying patients with
angle closure, and an understanding of the etiology of
narrowing is essential to determining which patients may
benefit from an LPI. n
Shuchi Patel, MD, is director of Glaucoma
Services and an assistant professor at Loyola
University Medical Center in Maywood,
Illinois. Dr. Patel may be reached at
[email protected].