MICS?
(24.09.2013)
(http://www.ophthalmologymanagement.com/articleviewer.aspx?articleID=108643)
(www.karmayog.org)
Two key opinion leaders debate the pros and cons
of microincision cataract surgery.
By Paul
S. Koch, MD, and Robert J. Weinstock, MD
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About the Authors: Paul S. Koch, MD, is editor emeritus of Ophthalmology Management and |
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Robert J. Weinstock, MD, is a cataract and |
Micro-incision cataract
surgery known as MICS has made inroads into ophthalmic surgical suites, but
the approach isnt without controversy. Advocates say that because MICS uses
smaller incisions than the traditional technique, it causes less trauma to the
eye, reduces the likelihood of postoperative astigmatism and carries fewer
risks of dry eye and other postoperative problems. The technique and equipment
MICS requires are the same as the conventional approach, so the learning curve
is virtually nonexistent.
Those
who take the opposite view note that few IOLs are suitable for MICS, the
smaller incision is more prone to uneven edges and irregular healing, and may
actually restrict a surgeons ability to manipulate instruments inside the
capsule, and the improvement over the conventional approach is too incremental
to merit broad acceptance.
Diving
deeper into the debate are two well-respected surgeons: Paul Koch, MD, editor
emeritus of Ophthalmology Management and medical director of Koch Eye
Associates in Warwick, R.I., taking the position that MICS is not ready for
prime time; and Robert J. Weinstock, MD, a cataract and refractive surgeon at
the Eye Institute of West Florida in Largo, Fla., arguing for MICS.
MICS DEFINED
Micro-incision
cataract surgery utilizes incisions ranging in size from 1.8 mm to 2.4 mm vs.
2.7 mm to 3.2 mm for traditional surgery. The smaller incision can accommodate
phaco tips as small as 1.8 mm in diameter. Two types of MICS exist.
Coaxial, or C-MICS
This
approach most closely resembles traditional cataract surgery. Incision size can
range from 2 mm to 2.2 mm. The phaco tip enters through a primary incision. A
second incision, smaller than 2 mm, accommodates the chopper tool. High
vacuum levels are possible with advanced fluidics, and power modulation
generates less heat than in conventional phacoemulsification.
Bimanual, or B-MICS
This
more advanced approach separates irrigation from phacoemulsification and
aspiration, allowing for superior control of fluid dynamics, advocates say. A
steady flow of irrigation into the anterior chamber allows for highly
controlled manipulation of the phaco handpiece and nuclear particles.
The
sleeveless irrigating chopper acts as an additional instrument inside the eye
by directing particles to the phaco tip, whereas in coaxial surgery the
irrigation tends to repel lens material away from the phaco tip. B-MICS is
faster, uses less phaco energy, causes less endothelial cell loss and less
postoperative inflammation and promotes faster healing and visual recovery,
according to its proponents.
ENOUGH IOL OPTIONS?
Q Do surgeons have enough IOL options to broadly embrace MICS?
Dr. Koch: Im not sure how many
lenses can be used with MICS. I know there are a handful, including the Akreos
from Bausch + Lomb Surgical (Aliso Viejo, Calif.). But with the traditional
phaco incision, you have the freedom to use any IOL you want.
Dr. Weinstock: We
do not have a lot of lenses right now can go through a 2.2-mm incision. With a
good wound-assisted injection technique, the AcrySof (Alcon, Forth Worth,
Texas) can go through that incision. The Akreos MICS platform can actually
easily go through a 2.2-mm incision, and with wound assist it can actually go
through a 1.8-mm incision. So the arsenal of lenses available to go through
these smaller wounds is already beginning to expand and will continue to
expand.
WOUND CLOSURE
Q How can wound management during IOL injection influence
outcomes?
Dr. Weinstock:
Some lenses, such as the Crystalens (B + L Surgical) and the multifocal
intraocular lenses require a slightly larger incision, but there is some merit
in doing MICS and then enlarging the wound for the IOL at the end of the
procedure. With this approach, you are operating through a smaller wound with a
more closed and sealed chamber and more stability in the chamber during the
most critical parts of the surgery, when complications often occur.
In
my experience, that adds an element of increased safety and can reduce
complications by having the smaller, tighter wound where the fluid dynamics are
more predictable and under the surgeons control.
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Why I prefer B-MICS over conventional surgery By Robert Weinstock, I am a huge believer in B-MICS because it Think about what Thats not to say |
Dr. Koch: When you make an
incision with the blade, you have perfectly smooth and sharp edges to the
incision, and it seals very nicely. If someone is tempted to squeeze or force
in an injector through an incision that is too small, to fit it into the eye,
the edges of the incision necessarily have to rip. This will create an
irregular contour, and that will damage the water tightness of the incision.
Were more likely to get a nice seal on the incision if we dont have to damage
it while injecting the lens.
PHACO BEHAVIOR
Q How does phaco behavior differ between conventional cataract
surgery and MICS?
Dr. Weinstock: I
use exclusively bimanual sleeveless 19-gauge instruments through a pair of
trapezoidal 1.4/1.6 incisions 80º apart. Howard Fine taught me this incredibly
refined, elegant and controlled way of removing cataracts a decade ago.
This
setup is the right balance of efficiency, chamber stability and safety for me.
And now, with the Akreos MICS, I can use a wound-assisted injection technique
and operate through these small wound start to finish.
I
have compared my B-MICS to C-MICS phaco time, case time, day one vision and
complication rate. B-MICS outperforms in all areas in my hands.
Dr. Koch: My preference is to
have as little resistance as possible when comes to removing lens fragments
from the eye. I use a 19-gauge needle with a 0.9-mm central opening, and I am
able to emulsify the nucleus to pieces that will fit out through that needle. If
I had a smaller needle, I would have to emulsify a little more. Were talking
very small quantities either way.
In
terms of surgical efficiency, with the larger sleeve I have the ability to put
in more fluid if I want to flush quicker and the ability to use a wider needle,
so I can aspirate out quicker. Im happy with that balance that we have.
INCISION SIZE
Q How does incision size influence outcomes in cataract surgery?
Dr. Koch: With a properly made
incision, either incision will close perfectly because for all practical
purposes, they are the same size. Were only talking a couple microns
difference in size. We saw a big difference when we went from 12-mm to 6-mm
incisions and 6-mm to 3-mm, but once youre at 3,000 µm or 2,400 µm, they
really are, for all practical purposes, the same size incision. If you make it
properly, its going to seal up just beautifully. I dont think that the
proponents of MICS can tout an advantage on the sealing of the incision,
assuming the surgeon using either technique is making a good one in the first
place.
Ive
assisted doing people doing MICS, and each time failed to see how it is
significantly better than surgery with a 3-mm incision. The ability to flush
out material is still the key to efficient surgery.
Having
the smaller sleeve means less inflow, and the smaller needle means less
outflow, but you do not necessarily have less resistance. A smaller incision
also restricts how the phaco tip moves through incision to the left and right.
With
the 3-mm incision, we are more likely to have unrestricted inflow, and the
larger phaco tip is more efficient in getting nuclear pieces out of the eye.
The larger incision also makes it easier to move the phaco tip to the left and
right within the eye.
Dr. Weinstock:
The larger the wound, the more corneal nerves you cut, which can cause dry eye
and postoperative dissatisfaction and complications for the patient. In theory,
the larger the wound, the higher the risk of endophthalmitis. Although thats
rare today, it is still out there, and endophthalmitis is a devastating event
for the patient and obviously for the surgeon.
In
addition, we see so many patients these days with floppy iris syndrome, and the
smaller wound does a great job of reducing iris prolapse compared to a larger
wound. Smaller wounds also create less leakage during the case and more chamber
stability in my opinion.
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Why MICS is not much better than what were doing now By Paul S. Koch, MD When I started doing cataract surgery in 1978, Each of those were |
LEARNING CURVE
Q Does MICS require a steep learning curve?
Dr. Weinstock:
The learning curve is almost completely transparent and simple especially in
C-MICS if the surgeon does his or her diligence in getting the instrumentation
and the phaco machine set on the right mode with the right settings. It is
nearly a seamless transition.
B-MICS
is a little more involved because youre learning to use your nondominant hand
even more. But again, the surgeons that Ive trained to do B-MICS have never
turned back to do coaxial phaco once they get the hang of it.
They
immediately recognize the benefits of separating the irrigation from the
aspiration and the phaco and the increased control and predictability they
experience inside the eye.
Dr. Koch: No, coaxial MICS does
not require a learning curve. Its the same technique with a small incision and
smaller tools. I dont think theres a learning curve at all. There is a
learning curve if you want to use bimanual MICS.
WHAT LIES AHEAD
Q Whats the next step in the evolution of cataract surgery?
Dr. Koch: If we can get to a
1.5-mm incision, then we have another revolution in cataract surgery. Ill give
you that right now. But we cant do that with the lenses we have now because
theyre too thick, or they have too much bulk.
Although
we already use IOLs with refractive indices that allow them to be made thin
thin enough to be rolled up into a micro-injector that fits into a small
incision someday, we will be able to marry everything together, so the
patient has what is essentially a needle stick in the eye rather than an
incision.
It
is only a matter of polymer chemistry and engineering thats keeping us from
getting there. So whether its the engineering of a very, very thin and
rollable lens or whether its the chemistry of a lens of a certain refractive
index that will be optically pure and yet have very little bulk, I believe
thats where the future of the next incision revolution lies.
Dr. Weinstock:
The logical next step here is to automate the surgery, like were doing with
lasers, and reduce the risk of complications, such as capsular tear or damage
to the iris or damage to the zonules or the cornea, as well as decreasing
problems such as surgically induced astigmatism, which becomes significant; the
larger the wound is, the more surgically induced astigmatism there is.
The
next level eventually maybe its two or three levels from now needs to be a
combined energy effort across our industry to push toward two separate 1-mm
incisions, one for irrigation and one for aspiration; complete laser
disintegration of the lens, requiring minimal need for phaco; and then
injecting some type of soft jelly-like biocompatible material that hardens or
can be adjusted to the appropriate refractive index and power once its inside
the eye. Then, we would truly be approaching the safest, least invasive and the
most precise procedure possible.
When
thats going to be, I dont know, but I think we need to set our sights on that
and incrementally move in that direction. Staying with the 3-mm incision ad
infinitum is clearly not going to achieve that goal.
CLOSING ARGUMENTS
Q So is MICS ready for prime time?
Dr. Weinstock: I
bet the same question was asked when we went from intracapsular to
extracapsular surgery or when it went from extracapsular to phaco.
What
defines prime time? In my mind, its defined by when the technology has matured
enough that the machines and handpieces and instrumentation have been modified
or developed or engineered to the point that they are safe for the everyday
surgeon to use.
I
truly believe, whether its C-MICS or B-MICS, the phaco machines we have today
are highly evolved to where, if the surgeon wants to make the transition to
smaller-incision surgery, the technology is there to do so. Were not talking
about entry-level, first-generation handpieces or phacoemulsification software.
We really have the tools we need to do this successfully without any risk.
For
that reason alone, I believe MICS is ready for prime time, and the fact that we
do have lenses that can go through these wounds makes it so in a majority of
cases, you truly can operate start to finish through a 2.2-mm or 1.8-mm wound
the latter if youre using the Akreos MICS with a wound-assist technique.
Dr. Koch: Again, my position is
that C-MICS, for all practical purposes, is the same thing as conventional
surgery, because reducing the incision only 600 µm, which is 300 µm to the left
and 300 µm to the right of the existing incision, is a tiny, tiny tolerance.
I
have not been convinced that it offers any advantage over what Im doing now, I
think MICS may actually restrict my ability to remove a cataract through a
large-bore needle.