It�s a delayed complication that can take cataract surgeons by
surprise�spontaneous bag-IOL dislocation years after the original
surgery. For many ophthalmologists, the problem comes out of the
blue, especially considering the routine nature of the
procedure.
Alan S. Crandall, MD, professor of ophthalmology
at the University of Utah, Salt Lake City, and Nick Mamalis, MD,
director of the university�s ophthalmic pathology laboratory, first
described the phenomenon in 1999 when they recognized spontaneous
bag-IOL dislocation years after cataract surgery.
It
continues to be a problem. This past February, a patient came to Dr.
Crandall�s practice complaining of a sudden �white-out� for 20
minutes. The next day, his vision was poor. �Other patients complain
of a classic jiggling in their vision,� Dr. Crandall said. �It comes
on so suddenly that many patients mistake it for a stroke or retinal
tear. When we first saw this, we were puzzled because many of the
symptoms are subtle. Now we recognize it quickly.�
Dr.
Crandall has published on the link between pseudoexfoliation and
late IOL dislocation, and the feedback he receives from cataract
surgeons all over the country indicates that dislocated IOLs are
still an issue. Yet much about the problem remains unknown,
including risk factors and incidence.
Diagnosing the Problem
Before
malpositioned IOLs can be surgically managed, they first must be
detected. Symptoms such as blurry vision and �jiggling� of the lens
are immediate red flags that the patient may be experiencing a
classic case of late bag-IOL dislocation.
The diagnosis of
pseudophacodonesis or IOL subluxation is made during a dilated
slit-lamp examination. David F. Chang, MD, clinical professor of
ophthalmology at the University of California, San Francisco,
cautions that diagnosis can be complicated by the fact that the
position of a dislocated bag-IOL can shift, depending upon whether
the patient is seated or supine. �Depending on the extent of the
zonular loss, the bag-IOL may simply exhibit pseudophacodonesis, or
a lateral subluxation. However, if most of the zonules are gone, the
bag-IOL may reside just behind the iris when the patient is sitting
at the slit lamp, then descend back to the mid vitreous when the
patient lies down,� he noted. �The surgeon may not realize this
until the patient is under the operating
microscope.�
Surgical
Management
For mild cases, ophthalmologists may want to
consider a conservative approach, said Uday Devgan, MD, assistant
clinical professor of ophthalmology at the University of California,
Los Angeles. �The anatomic center of the eye is not necessarily the
visual axis, and any shift in the lens can impact the quality of
vision,� he pointed out. �If there is only mild decentration and
patient satisfaction is not too adversely affected, then it may be
judicious to defer surgery.
�On the other hand,� he added,
�if patients are symptomatic, where they are actually seeing the
edge of the IOL or their vision is poor because they are not looking
through the center of the lens, then surgery may be in
order.�
When Surgery Is
Essential
Depending upon the degree of vitreous
liquefaction, if the bag-IOL is almost completely dislocated then
surgery is necessary and should be done in a timely manner.
Dr. Chang recalled one patient with pseudoexfoliation whose bag-IOL
complex was partially subluxated posteriorly at the slit lamp, but
had dropped down onto the retina by the time of his scheduled
surgery two weeks later. Dr. Crandall has seen the same phenomenon
occur in just two days.
Dr. Crandall�s surgical management
guidelines are straightforward. First, �get it done.� Second, make
every attempt to know the position of the lens prior to surgery so
that a surgical plan may be developed. Finally, be ready for any
contingency, including vitrectomy, suturing and pars plana
vitrectomy.
Sophisticated
Techniques
Paracentesis. The most
challenging cases are those in which the bag-IOL complex has
descended posteriorly into the anterior vitreous. In some cases, the
bag-IOL will migrate forward to the pupil plane as one empties the
anterior chamber by depressing the paracentesis edge. But Dr. Chang
notes that explantation can be difficult even when the bag-IOL is
sitting just behind the pupil. �Bag-IOL dislocations are very
different from situations where a subluxated IOL still has posterior
capsular support, and we can readily grasp a haptic or hook the
haptic-optic junction,� he explained. �Here, the haptics are
inaccessible and encased in a free-floating 10-millimeter diameter
phimotic bag. Furthermore, with pseudoexfoliation, the pupil is
often small, and you will want to use iris retractors because of the
need to explant the entire bag�not just the IOL,� Dr. Chang
said.
Posterior assisted levitation. In
cases where the bag-IOL complex has descended into the anterior
vitreous, and is therefore not supported, Dr. Chang performs a
variation of the posterior assisted levitation technique1
first popularized by Charles D. Kelman, MD.
He first inserts
a Viscoat cannula through a pars plana sclerotomy 3.5-mm behind the
limbus. �Injecting a dispersive viscoelastic behind the IOL will
immediately provide supplemental support so that it does not descend
further with manipulation,� Dr. Chang said. Next, under direct
visualization with the operating microscope, he uses the cannula tip
to elevate the bag-IOL complex into the pupillary plane, and to tip
one end up through the pupil where the optic can be grasped with
toothed forceps. �Because the fibrotic bag is so wide, it helps for
the levitating instruments to have the more posterior angle of
approach afforded by the pars plana sclerotomy,� he said.
�Obviously, IOLs in the posterior vitreous cavity should be
retrieved by a vitreoretinal
surgeon.�
Suturing. Where the bag-IOL
complex is loose, but has not dislocated posteriorly or
peripherally, �it is possible to secure the bag-IOL without losing
vitreous,� said Dr. Chang. �You can use a double-armed 9-0
polypropylene suture to suture each haptic to the sulcus. One of the
needles will pass right through the peripheral bag and behind the
haptic, so that it doesn�t have to be externalized.�
Pseudoexfoliation as a Risk Factor
Little
is known about what causes delayed bag-IOL dislocation after
cataract surgery, but Dr. Crandall did report that patients with
pseudoexfoliation syndrome were at risk for experiencing a late
spontaneous dislocation of the IOL within the capsular
bag.
�This raises the question,� said Dr. Chang, �of whether
placing capsular tension rings (CTR) in patients with
pseudoexfoliation will prevent late bag-IOL dislocations. If I have
patients with pseudoexfoliation in whom the zonules appear to be of
normal strength, I don�t place a ring. However, if there is any sign
at all of zonular weakness, I suggest using a CTR because it should
resist the forces that produce capsulophimosis and centripetal
zonular traction.�
Dr. Chang noted that if there is major
zonular loss, then a CTR alone will not stabilize the bag.
Unfortunately, the Cionni-modified ring and the Ahmed capsular
tension segment, which would allow scleral suture fixation of the
ring, are not available in the United States.
Other Preventive Measures
Dr. Chang notes
additional steps to consider for lowering the risk of late bag-IOL
dislocation.2 He suggests using an acrylic optic because
of the decreased tendency for anterior capsular fibrosis and
capsulorhexis shrinkage as compared with silicone. He also
recommended selecting a three-piece acrylic IOL because the PMMA
haptics are stiffer and have greater rigidity compared with
single-piece haptics. �Finally,� he said, �you should secondarily
enlarge a small diameter capsulorhexis in pseudoexfoliation patients
at the end of surgery. If you already see fibrosis of the
capsulorhexis edge developing one month after cataract surgery in
these patients, you may want to make relaxing cuts in the edge with
the YAG laser.�
Dr. Devgan suggested using modern generation
lenses with haptics that keep the lenses well centered, and lenses
that have a uniform power from the center to the edge. �Thus,
decentration by even 2 mm doesn�t necessarily cause a significant
degradation in image quality�and this is a key point,� he
said.
�The diameter of the capsulorhexis should be slightly
smaller than the diameter of the IOL optic,� he added. �If I have a
6-mm optic, I will make a 5.5-mm diameter capsulorhexis. This allows
the edge of the capsulorhexis to surround, and hold in place, the
lens optic.�
Recognition Is
Vital
Dr. Chang concluded that because it takes so long
for spontaneous bag-IOL dislocation to develop in patients with
abnormal zonules, it will be years before we can assess whether
these preventive measures will help. Added Dr. Crandall, �The
important thing to stress is that while we don�t have the answers to
prevent the problem, it is vital that ophthalmologists recognize
late-dislocated IOLs�especially in patients with
pseudoexfoliation�and either treat the patient or refer them to an
expert.�
______________________________
1 Chang, D. F. J
Cataract Refract Surg 2002; 28:1515�1519.
2 Chang, D. F.
Ophthalmology 2002;109:
1951�1952.
______________________________
Drs.
Crandall and Devgan have no related financial interests. Dr. Chang
is a consultant for AMO and has received educational travel support
from Alcon, but has no financial interest in any product.