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February 2006

Clinical Update: Cataract
Coaxial Microphacoemulsification: A Primer
By Jean Shaw, Contributing Writer

The siren song of ever-smaller incisions keeps calling cataract surgeons onward. Two years ago, bimanual microphaco seemed full of promise. But a growing number of cataract surgeons have become disenchanted with this microincisional approach and its attendant learning curve and potential complications.

Now, with the development of a new ultrasound sleeve that allows for ultra-small incisions through a traditional coaxial approach, microphaco appears to be developing a new lease on life. And coaxial microphaco, as this new approach is known, is finding fast acceptance among expert cataract surgeons. “I use it with at least 95 percent of my cases,” said Robert H. Osher, MD, professor of ophthalmology at the University of Cincinnati and medical director emeritus of the Cincinnati Eye Institute. “The few patients I don’t use it in are those with extremely low cell counts, such as Fuchs’ dystrophy, and those who have undergone a 16-incision radial keratotomy. But I use coaxial microphaco with virtually everybody else. It has become my procedure of choice.”

Samuel Masket, MD, in private practice in Los Angeles and clinical professor of ophthalmology at the University of California, Los Angeles, concurred. “It’s essentially the only way I do cataract surgery now—and I made the transition in a relatively short period of time.”

Microphaco Basics
Bimanual microphaco. Bimanual microphaco typically requires three incisions. For cataract removal, the surgeon makes two side-port incisions roughly 1.2 millimeters to 1.4 mm in length and uses an irrigating chopper in one hand and the sleeveless phaco device in the other. For IOL insertion, most surgeons make a third incision 2.8 mm to 3 mm in length.

Coaxial microphaco. In coaxial microphaco, the surgeon makes a 2.2-mm incision (along with a 1-mm stab incision for the second instrument). Phacoemulsification is performed using Alcon’s small-diameter UltraSleeve and the company’s Infiniti system. A full-size, single-piece AcrySof IOL can be inserted without enlarging the incision, and a separate incision is not required.

Issues to Consider
There are several issues to consider in comparing bimanual and coaxial microphaco:

Incision integrity. “Regarding coaxial microphaco, I became enamored with the fact that the phaco tip is covered with a sleeve,” Dr. Masket said. “With bimanual microphaco, the unsleeved rigid round tubes induce distortion of the small slit incisions. Because there is no sleeve to cushion and fill the incisions, they tend to be either too small or too large. If they’re too small, the tissue distorts and the incisions will ‘fishmouth,’ causing leakage after the instruments are removed from the eye. On the other hand, if the incisions are too large, fluid leaks around the tubes during surgery, causing fluctuation of the chamber depth.”

In contrast, with coaxial microphaco, “the sleeve acts as a buffer and won’t distort or ‘fishmouth’ the tissue,” Dr. Masket said. “The incisions self-seal and will not leak post- or intraoperatively.”

He added, “Originally, I liked the concept of bimanual microphaco from the viewpoint of reduced incision size and the advantage of nonopposing and nonrepelling fluidics, but disappointment with incisions led me away from the technique. I spent much more time managing the incisions at the close of surgery than was reasonable.”

Dr. Osher noted that the coaxial microphaco incisions can leak before you hydrate, “but as soon as you hydrate they stop leaking. That’s different than the bimanual microphaco incisions—those are not as consistently competent.”

Fluidics. A number of cataract surgeons have complained of poor chamber control with bimanual microphaco, as the available infusing choppers can’t provide enough fluid flow to keep the chamber formed.

With coaxial microphaco, however, the fluidics “are basically the same [as those seen with standard phaco],” said Dr. Masket, with one caveat: Because the UltraSleeve is more rigid, it is necessary to raise the bottle height (see “Tips on Technique”).

Temperature protection. Because of its sleeveless technology, bimanual microphaco raises the risk of thermal injury to the wound. Most cataract surgeons have avoided this by using systems that deliver very short bursts of energy.

In contrast, the UltraSleeve “provides insulation and allows enough aspiration flow rate to cool the tip,” said Dr. Osher. “Moreover, the advantage of the ABS [aspiration bypass system] hole is only possible with a coaxial system.”

IOL selection. At present, no IOLs on the U.S. market are approved for microincisional surgery. As a result, with bimanual microphaco, the surgeon must either enlarge one of the initial incisions or make a third incision for IOL insertion.

With coaxial microphaco, the surgeon can insert most standard foldable IOLs through the UltraSleeve (see “Tips on Technique”). “I don’t have to compromise on IOL selection,” said Dr. Osher. “I can get perfect centration, low PCO [posterior capsular opacification] rates, macular protection, toric control or multifocal—in other words, I can get all of the selective advantages of the IOLs on the U.S. market.”

Learning curve. Supporters of bimanual microphaco argue that having separate infusion and phaco instruments allows for greater control. However, many cataract surgeons are un-comfortable with the learning curve needed to master the bimanual approach. Coaxial microphaco, on the other hand, can be adopted very quickly.

Clinical Results
Incisions intact.
Dr. Osher noted that he recently treated 100 consecutive patients with coaxial microphaco. “Following surgery, 99 percent of those incisions were watertight. One incision required a suture.” UCVA and corneal clarity on the first postoperative day were excellent in all patients.

Astigmatism reduced. Following his long-standing interest in surgically induced astigmatism, Dr. Masket studied the astigmatic effects of coaxial microphaco in 16 patients who had bilateral cataracts. He performed the 2.2-mm coaxial microphaco incision in one eye and a standard 3-mm temporal corneal incision in the fellow eye.

Keratometry was performed before surgery and at six weeks postoperatively. There were no surgical complications. The surgically induced astigmatism was 0.10 D for the eyes in the coaxial microphaco group and 0.32 D for the eyes in the standard incision group.¹ “These differences were highly statistically significant,” Dr. Masket said.

Conclusion on Coaxial?
Overall, Dr. Masket said, one of the strongest arguments in favor of coaxial microphaco has to do with incision architecture. “One can easily make the incision square in its surface architecture—the width and length can be the same. We know from the earlier work of Paul Ernest that this is the most physically stable wound architecture.” He noted that this concept is potentially quite important, as recent studies have indicated that traditional 3-mm clear corneal incisions may be unstable after surgery and could allow wound leakage, increasing the risks for postoperative infection.

And Dr. Osher concluded, “For me to make a significant change in how I operate, I want increased efficiency, optimal fluidics, temperature protection and increased incision competency. I don’t want to have to enlarge an incision or make a separate incision for my IOL of choice. I don’t want to buy all new instruments. and I don’t want a steep learning curve. Coaxial microphaco addresses these issues.”

Dr. Masket has no related financial interests; Dr. Osher is a consultant for Alcon.

1 Results presented at the 2005 ESCRS meeting in Lisbon, Portugal.

Tips on Technique

When it comes to the surgical techniques, the differences between standard coaxial phaco and coaxial microphaco are few and relatively subtle. Those of note include:

IOL implantation. Dr. Osher has developed the following steps for IOL implantation:

  • Load the IOL into the cartridge so that the haptics open like a book.
  • Firm up the eye and apply countertraction. To do this, he puts a second instrument in the stab incision.
  • Inject the IOL bevel down within the incision.
  • Inject the lens quickly so it doesn’t get stuck in the incision.
  • Don’t use a typical two-handed injector. Instead, use a one-handed, plunger-style injector. Dr. Osher suggested those from ASICO and Rumex, as well as the one he designed for Duckworth & Kent.

Bottle height. The sleeve used in coaxial slightly restricts fluid flow into the incision, but raising the bottle height increases the flow pressure. “This is an important point,” Dr. Osher said. “I conducted an experiment comparing all of the different choppers, with the bottle at 100 centimeters. With bimanual microphaco, I got 20 cc to 60 cc per minute [depending on the chopper]. With coaxial microphaco, I got about 85 cc per minute—slightly less than regular phaco but a big improvement over bimanual. As a result, I raise the bottle around 25 percent, just to play it safe. It gives me a completely stable chamber.”

Choice of instrument. “Presently, there isn’t a great steel blade that creates a consistent 2.2-mm incision,” Dr. Masket said. “From my own experience, I know that there is a risk of stretching the tissue if the incision is smaller than 2.2 mm. But I do have a diamond blade that works perfectly and does provide a genuine and consistent 2.2-mm incision.” He added that “the standard capsulorhexis forceps may not work—instead, one may use those forceps made for bimanual microphaco.”