October 2007

 

CATARACT/ IOL

 

Perfect incision size


by Matt Young EyeWorld Contributing Editor

 

 

Study takes a closer look at the incision size

Source: David F. Chang, M.D.

Since the dawn of phacoemulsification, ophthalmologists have been striving to achieve smaller incisions to minimize astigmatism and optimize wound healing.

Bimanual microincision phacoemulsification is one of the latest attempts to do just that through incisions as small as one millimeter in length.

Yet a new study by Sung Chur Moon, M.D., Ph.D., Oregon Eye Institute, Eugene, Ore., found that smaller incisions didn’t induce the least amount of astigmatism. Rather, 2.5- mm incisions induced more astigmatism than 3-mm incisions. The study was published in the Korean Journal of Ophthalmology. A review of this study also was published in the June issue of EyeWorld. Despite the fact that this study involved coaxial phacoemulsification rather than bimanual microincision, it did raise some interesting questions about the bimanual procedure with regard to incision size. For instance, are smaller incisions, like the ones created with bimanual surgery, ideal after all? EyeWorld put this question, and others involving bimanual surgery, to I. Howard Fine, M.D., clinical professor, Casey Eye Institute, Oregon Health & Sciences University, Portland, Ore., who was a co-author of the Korean Journal study and has been a consistent advocate for the bimanual approach.

Adding a third incision

In his study, Dr. Moon noted that the 3.0-mm incisions were not stretched as much as the 2.5-mm incisions in order to place the IOLs. Hence, stretching could have contributed to the difference in astigmatism induction between the two groups. Dr. Fine said that incision size for this study was not measured after insertion to determine the effect of stretching on length. But in a previous study, he said, incisions that were 2.5 mm were stretched to 2.8 mm. As a result, smaller incisions would only be suspect in astigmatism induction if they were stretched. What is the possibility of stretching one of the microincisions—with respect to bimanual? The possibility does exist because surgeons must either enlarge the microincision, or create a third incision for the IOL. “Since the [micro] incision is tighter than most incisions and since it doesn’t have a sleeve, that incision is more susceptible to distortion and tearing,” Dr. Fine said. “It won’t seal as well if you enlarge it.”

As a result, Dr. Fine suggested making that third incision for the IOL with bimanual. His is about 2.8 mm, he said. “You shouldn’t be macho about how small incision you can get a lens through,” Dr. Fine said. “Make an incision of adequate size so you’re not distorting it.”

Hence, the Korean Journal study does not detract from the long, noble history of striving for smaller incisions, including the latest bimanual approach. Rather, it suggests that small incisions—even with bimanual—may contribute to the incidence of astigmatism if proper care isn’t taken in constructing the incisions. Dr. Fine added that even the minute 1-mm sideport incisions themselves—aside from any enlargement that some chose to pursue—need to be properly constructed. Some surgeons just make a quick in-and-out incision without giving it much thought, he said.

Even in his own clinic, Dr. Fine said he realized that there was a time than these side port incisions were not ideal.

“We took more care in the way we constructed 1.1-mm side port incisions,” Dr. Fine said.

A firm bimanual believer

Dr. Fine noted that until lenses are able to fit through incisions smaller than coaxial ones, the bimanual technique may not gain much greater acceptance in the United States. Once that happens, bimanual may demonstrate a clearer astigmatism advantage over coaxial. To illustrate this point, Dr. Fine noted a complicated cases of a badly decentered lens in which four 1-mm side port incisions were made to reposition the lens. Further, two 1.1-mm incisions were made to removethe ophthalmic viscosurgical device. “Pre-operative K-readings and refraction were exactly the same as post-op, documenting the fact that here’s an eye with six microincisions and no change in astigmatism,” Dr. Fine said. Of course, there are currently other benefits to bimanual, especially with respect to fluidics, Dr. Fine said. “All the fluid is coming in through one side and leaving through the other,” he said. “You never get competing currents around the phaco tip. We can accomplish things with bimanual we can’t with coaxial because every place we bring the [coaxial] tip a stream of fluid pushes nuclear material away. If we have a rupture in a capsule or lose zonules, bimanual is advantageous.”

Editors’ note: Dr. Fine has financial interests with Advanced Medical Optics (AMO, Santa Ana, Calif.), Bausch & Lomb (Rochester, N.Y.), and Alcon (Fort Worth, Texas). Dr. Moon has no financial interests related to his study.

Contact Information

Fine: 541-687-2110, hfine@finemd.com

Moon: 1-800-452-2040, sungemoon@hanmail.net

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