CATARACT/ IOL |
The debate rages on: precision versus care by Matt Young EyeWorld Contributing Editor |
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Diamond knives, cataract chart 1
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Over
the years, not much may have changed about diamond knives for cataract
surgery—at least in terms of fundamentals. They’re
sharp and they can lead to excellent incision construction when handled
properly. Furthermore, as cataract surgery becomes more like refractive surgery,
surgeons may wish to revisit the concept of the diamond knife if they’re
not already using them. That’s because while diamond knife fundamentals are the same, surgery
has gotten more complex in order to achieve better results. Consider bimanual microincision phacoemulsification, for instance. This procedure,
which has separated irrigation and aspiration during surgery, is heralded
by some as a great way to create microincisions, which of course can lead
to less induced astigmatism. However, has been criticized by others for ompromised
wound architecture. Enter the diamond knife. “Absolutely the results are better with a
diamond knife,” said Mohan Rajan, M.D., Rajan Eye Care Hospital, Chennai,
India. Dr. Rajan said his clinic has documentation that bimanual phacoemulsification
(also known as MICS, microincision cataract surgery) is better with the diamond
knife. “Wound closure is better,” he said. “Predictability
is so good.” He continued: “If you do 100 cataract cases, 70
may be very good with metal blades. But if you do 100 with diamond blades,
then 100 will be very good.” The architecture of the diamond knife itself may be responsible. “A
diamond knife, because of its trapezoidal configuration, produces less distortion
when it goes into the anterior chamber,” Dr. Rajan said. “The
diamond knife cuts very nice and smooth. So even if you’re shoving
the instrument, the [wound] edges are not distorted.” Meanwhile, I. Howard Fine, M.D., clinical professor, Casey Eye Institute,
Oregon Health & Science University, Portland, has been a leading proponent
of bimanual microincision phacoemulsification. In describing his technique, Dr. Fine noted the use of a diamond knife. “A
Paratrap diamond keratome (Mastel Precision Surgical Instruments, Rapid City,
S.D.) is used to create 2 1.2 mm clear corneal incisions 30 to 45 degrees
from the temporal limbus and 60 to 90 degrees from each other,” Dr.
Fine reported in the March 2004 issue of the Journal of Cataract & Refractive
Surgery. He adds: “Although coaxial phacoemulsification is an excellent procedure
with low amounts of induced astigmatism, bimanual phacoemulsification offers
the potential for truly astigmatic neutral incisions.” And those incisions
are created with diamond knives.
Counterpoint
Nonetheless, some research continues to be critical of bimanual phacoemulsification
in comparison with coaxial procedures—regardless of the type of blade
usage. In the March 2007 issue of the Journal of Cataract & Refractive Surgery,
John P. Berdahl, M.D., Duke University Eye Center, Durham, N.C., compared
bimanual phaco with traditional coaxial and microincisional coaxial procedures.
Each grouping was allocated five human cadaver eyes, whose wounds were studied
after phacoemulsification using a combination of simulated IOP raising and
lowering and India ink movement. “Spontaneous wound leakage was evident in all 5 eyes having bimanual
phacoemulsification, in 1 eye (20%) having standard coaxial phacoemulsification,
and no eye having microincision coaxial phacoemulsification,” Dr. Berdahl
reported. “Scanning electron microscopy showed increased endothelial
cell loss and greater compromise to Descemet’s membrane with bimanual
phacoemulsification than with standard coaxial phacoemulsification or microincision
coaxial phacoemulsification.”
Dr. Berdahl concluded that wound stress and morphology was worse in the bimanual
group. Still, other ophthalmologists have commented that wound leakage is
not entirely bad—that leaks may help to cool thermal energy from phacoemulsification.
Clearly, though, there is more to these procedures than whether or not a
diamond knife is used. But if your clinic is benefiting from bimanual phacoemulsification, it may
also benefit incrementally from diamond knives. Tat-Keong Chan, M.D., Singapore
National Eye Centre, said the incidence of wound dehiscence is higher in
bimanual surgery, but the type of instruments you use matters. “You
need a sharp blade—not a blunt one,” Dr. Chan said, and a diamond
is the sharpest you can get. “And square incision design is better
than a rectangular one. He added that “stromal hydration is preferable
for water tight incisions, but whenever in doubt, put in a suture.”
If a steel blade is very sharp, it also can produce good results, he said.
Further, a two-step incision is better than a single-plane incision, and
steel blades may be preferable in that regard. So while diamonds are very
sharp and precise, how you configure the wound may be more important, he
said. “Not all incisions are created equal,” Dr. Chan said. A 2004 survey of ASCRS ophthalmologists found that surgeons still preferred
metal blades to diamond ones by a two-to-one margin. Past reasons cited by
ophthalmologists for metal preference have included the fact that they are
less expensive (at least in terms of initial investment) and can be maintained
more easily in a busy clinic than diamond knives, which have to be handled
with extreme care. If not, surgeons have said diamonds can easily become
dull. All in all, diamonds are exquisitely sharp, which help create excellent incisions.
The importance of incisional perfection is enhanced now that patients are
expecting excellent vision after cataract surgery. They don’t need
any interference from induced astigmatism. Excellent wound architecture also
is important given the leaky challenges of new phacoemulsification techniques
like bimanual phacoemulsification. However, certain wound architecture—which may be easier at times with
metal blades—could be more important than a perfectly sliced incision.
And with many surgeons still preferring metal blades, the diamond still is
in need of a broader fan base. Editors’ note:
Dr. Fine has financial interests with Advanced Medical Optics
(Santa Ana, Calif.) and Bausch & Lomb (Rochester, N.Y.).
Dr. Berdahl has no financial interests related to his study.
Drs. Rajan and Tan have no financial interests related to their
comments. Contact Information Berdahl: 919-684-6611, info@dukeeye.org Fine: 541-687-2110, hfine@finemd.com Rajan: +65 6254 6330, rajaneye@vsnl.com Tan: snecdt@pacific.net.sg.
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