October 2008




The debate rages on: precision versus care

by Matt Young EyeWorld Contributing Editor


Diamond knives, cataract chart 1

Diamond knives, cataract chart 2


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.


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.

The debate rages on: precision versus care The debate rages on: precision versus care
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