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EyeWorld - CATARACT - Preventing PCO

F EBRUARY 2011

CATARACT/ Preventing PCO

IOL
by David Spalton, F.R.C.S.
ESCRS Ridley Medalist David Spalton, F.R.C.S.,
St. Thomas Hospital, London, discusses current
and future methods of PCO prevention

Two or 3 years ago,

Despite
people thought that
advances in IOL posterior capsular
design and opacification (PCO) had
surgical
become a thing of the
technique,
posterior past. Although it's less of
capsule a problem now, it's still a
Cellular PCO Source:
opacification significant clinical issue,
(PCO) continues Mostafa A. Elgohary, M.D.
especially with regard to
to be a problem
for cataract the use of premium
surgeons. lenses and
Although the
accommodative lenses.
YAG laser is an
PCO is one of the limiting

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 easy, factors in the use of
"miraculous" fix
these lenses. Patients
for patients with
PCO, the rare with diffractive multifocal
creation of a lenses are susceptible to
retinal tear or very small amounts of
detachment and
PCO. Diffractive lenses
the potential for
permanent post- divide the light into two
YAG floaters foci, which means there's
Fibrotic PCO Source:
makes its use
only about 40% of light
less than ideal. Mostafa A. Elgohary, M.D.
A treatment that in each focus; therefore,
could eliminate the patient needs all the light he or she can get. A
PCO would help bit of PCO knocks that down considerably.
improve surgical
outcomes and It's a problem for accommodative lenses as well
improve the
because when the bag fibroses, it seems to stop
chances of one
day achieving the lenses from moving. Of course you can't refill
an injectable the capsular bag with an elastic polymer because
crystalline lens
it develops PCO, too.
substitute that
could restore
Lens design and surgical methods
accommodation.

At the moment, PCO is a multifactorial problem.

In this month's
column, David In order to prevent PCO, changes in IOL material
Spalton, and design as well as various surgical techniques
F.R.C.S., reviews
and pharmacological methods to remove or
some of the
issues and
destroy lens epithelial cells have been prescribed.
research that A lens with a good, sharp square-edge profile is
are ongoing in necessary to prevent PCO. My colleagues and I
regard to
looked at the electromicroscopy of a lot of IOLs,
reducing or
potentially and we saw that the edge profile varies. Some
eliminating the manufacturers make good ones while others
occurrence of don't. That's an important point because some
PCO.

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 Richard lenses may be advertised as having a square-edge
Hoffman, M.D.
profile, but they're not all equally effective.
Column Editor
Hydrophylic lenses have a poorer square-edge
profile than those made of hydrophobic materials.
We developed a technique to look at square edges
with what's called environmental scanning
microscopy. You can look at a wet specimen in an
electromicroscope in its natural state. We could
image these lenses very clearly and measure the
sharpness of the edge using dedicated software
we developed.

Another factor that's important in PCO prevention

is having a 360-degree square edge barrier right
around the optic. A lot of lens designs have a
break in the barrier at the optic haptic junction
and that allows cells to escape onto the posterior
capsule. Everything in IOL design is a balance of
the pros and cons. If we're going to have a 360-
degree square edge, it tends to mean the lens has
to be slightly thicker, and that means we can't get
it through as small of an incision size. On the
other hand, if we want a lens for a very small
incision, the downside is we tend to get higher
PCO. In terms of surgical methods of PCO
prevention, making the capsulorhexis slightly
smaller than the optic of the implant is important.
Over 2-4 weeks after surgery, the capsule fibroses
and that fibrosis pushes the lens back onto the
posterior capsule and creates a mechanical barrier
on the posterior edge of the lens where the
square edge barrier is located. It forms a sort of

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 pressure barrier to the migration of epithelial
cells. In addition, if the rhexis is asymmetrical or
off of the lens implant, we don't get the same
efficacy in pushing the lens back against the
posterior capsule.

Dealing with lens epithelial cells

There are also pharmacological methods of

dealing with PCO, although fundamental problems
have been associated with many of them. One of
the concepts involves locking up the lens epithelial
cells in the equatorial capsule. The surgeon
performs a posterior capsulorhexis and prolapses
the optic through that or uses what's called the
bag-in-the-lens, a Belgian-designed lens. The
rhexis has to be 5 mm in diameter, it has to be
central, and there must be a concentric posterior
capsulorhexis. The lens is placed so that both
anterior and posterior rhexes lie in this groove in
the lens, and these eyes maintain an entirely clear
posterior capsule because there is no posterior
capsule. However, a recent report by Liliana
Werner, M.D., Ph.D., research associate professor,
ophthalmology and visual sciences department,
John A. Moran Eye Center, University of Utah, Salt
Lake City, showed these go on to develop massive
Soemmering's ring. While the posterior capsule is
clear, there's a downside, so this is not the answer
to PCO prevention.

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 Another concept concerns the killing of all the
epithelial cells in the capsular bag using a device
called the Perfect Capsule (Milvella, North Sydney,
Australia), which is held over the capsulorhexis by
a suction ring in the eye at the time of surgery.
The inside of the capsular bag is isolated and then
irrigated with a solution to kill the lens epithelial
cells. Once again, although it sounds like a good
concept, clinical studies have been rather
disappointing. The lens epithelial cells are
probably protected by remnants of overlying
hydrophilic cortical material so things like aqueous
solutions can't penetrate. Two years after surgery,
these eyes have the same amount of PCO as the
control eyes.

The idea of removing all of the cells from the bag

has also been explored using a variety of
instruments and techniques. The problem here is
that we have to remove the equatorial cells. If we
just remove the anterior capsule cells, the eyes
get more PCO. The reason for this is we reduce
the fibrosis in the anterior capsule so we restrict
the fibrosing force within the capsular bag. This
means we don't push the lens implant against the
posterior capsule as tightly as we would with a
fibrosed posterior capsule, so cells can get in and
cause PCO. The A.R.C. Laser (Nuremburg,
Germany) is a new device developed for cell
removal. It uses laser shockwaves, and we can
blast all the cells off the capsule, so we end up
with a capsule that is acellular as long as we can

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 go around for 360 degrees and treat it all. It also
seems to remove adhesion molecules. The
technology sounds quite promising and clinical
trials are ongoing in Germany at the moment. In
theory, though, the problem with this focal laser
treatment is if we miss a few cells, PCO could
develop. Another problem is we don't know if
there's any danger that the laser shockwaves
could damage the iris or the ciliary body.

In Britain, my colleagues and I recently tested this

cell removal idea by taking human post-mortem
capsular bags and growing them in a new
laboratory cultured model. It's the best model that
has been described so far and involves performing
surgery on a human post- mortem lens and
growing it in an incubator for weeks following the
operation. What we showed was if we take a pair
of eyes from the same patient, do the surgery, put
an IOL in each eye, and kill all the lens epithelial
cells in the fellow eye, 3 or 4 weeks post-op, we
would see that in the control eye, the IOL is
fibrosing into the bag, just as in a human eye. In
the treated eye, however, the lens wobbled. This
indicated that with the current lens design, we
need lens epithelial cells there to fix and stabilize
the IOL. If we are going to kill all the cells in the
bag, we have to radically change the design of the
lens implant. There are some fundamental
questions there, and no one knows what the long-
term consequences of killing all the cells in the
human eye are. Do we need the cell bed to

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 maintain the collagen and the elasticity of the
bag? Does removing these cells ultimately cause
degeneration of the capsular bag?

New ideas

Open-bag devices are a novel idea. Studies on the

Synchrony lens (Abbott Medical Optics, Santa
Ana, Calif.) have reported very low rates of PCO.
It seems there's a possibility that by keeping the
capsular bag open after surgery and allowing
circulation of aqueous into the capsular bag, we
may be removing cytokines and growth factors
and therefore we don't stimulate the lens
epithelial cells to proliferate in the same way.
There are a number of companies that are
involved in making such devices, although it's
entirely experimental at this point. We will also
have to see whether the Synchrony lens, when it
comes into standard clinical practice, continues to
have low PCO rates when it's being used by a lot
of surgeons. With the other three approaches to
dealing with lens epithelial cells all having
fundamental problems, the idea of opening the
capsular bag is different and worth exploring.

Editors' note: Dr. Spalton has no financial

interests related to his comments.

Contact information

Spalton: +44 020 7935 6174,

practice_manager2@davidspalton.com

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