Eyeworld

FEB 2012

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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78 78 EW REFRACTIVE SURGERY February 2012 Refractive editor's corner of the world Treating astigmatism with arcuate incisions by Faith A. Hayden EyeWorld Staff Writer How the femtosecond laser changes astigmatism management rcuate incisions (arcs) have been a mainstay of astigmatism man- agement for the past two to three decades. While the location of the arcs has changed over the years and nomo- grams have evolved to improve predictabil- ity, ultimately the results have still been variable. Arcs have also been plagued by their share of challenges. For example, the more central an arc is placed, the greater the chances are to create some irregular astigmatism. Limbal relaxing incisions (LRIs) are essentially arcuate incisions that are placed more peripherally. While LRIs do minimize irregular astigma- tism induction, their peripheral location decreases their overall effect. Will a laser-created arcuate incision improve our results? That's the promise of the new technology. However, the fem- tosecond technology has its own chal- lenges—increased cost and time to perform the procedure are the two most obvious ones. Yet if history is any indication (such as with excimer laser technology compared to radial keratotomy), if the results show improved outcomes, the costs will work themselves out and time efficien- cies will likely follow. A Kerry D. Solomon, M.D., refractive editor A stigmatism is extremely common in patients un- dergoing cataract surgery and is a critical factor in determining outcomes, quality of vision, and patient satis- faction. It's estimated that 70% of patients have half a diopter or more of astigmatism, and 40% have at least 1 D, yet not every cataract sur- geon practices astigmatism manage- ment. Limbal relaxing incisions (LRIs) for the treatment of astigma- tism are difficult for many surgeons and the results are variable, causing some surgeons to abandon the tech- nique altogether. But now ophthalmologists have in their armamentarium the fem- tosecond laser for cataract surgery, a disruptive technology that solves many of the problems surrounding manually made LRIs. "The femtosecond laser provides reproducibility, reduced variability compared with manual incisions, and it's almost impossible to perfo- rate the eye," said Eric Donnenfeld, M.D., co-chairman of cornea, Nassau University Medical Center, East Meadow, N.Y. "It's controlled by OCT [optical coherence tomogra- phy] data, so you can preset your desired depth of incision and get reproducible incisions that you can't get with a manual LRI." The problem with LRIs "We don't have a good, consistent way to do LRIs," said Kerry D. Solomon, M.D., director, Carolina Eyecare Research Institute, Carolina Eyecare Physicians, Charleston, S.C. "I know it's not consistent because everyone does it differently." Questions surgeons face that may discourage them from learning the LRI technique include which type of diamond knife to use, which nomogram is appropriate, how deep should the incision be, and how does one determine the depth of the cornea. "I think it's confusing for some surgeons," Dr. Solomon said. "Be- cause the results are inconsistent, I think there are a great many sur- geons who say 'Forget it.'" There's also an awareness issue, said Dr. Solomon. When ophthal- An example of an eye with an LRI to correct astigmatism Source: Samuel Masket, M.D. mologists first began performing corneal refractive surgery, less than a diopter of astigmatism was consid- ered not clinically significant. How- ever, with the invention of LASIK and PRK, refractive surgeons began to realize that by treating lower amounts of astigmatism, say 0.75 D to 0.50 D, 20/20 rates increased to above 90% of patients. "There isn't a LASIK or PRK sur- geon out there now who wouldn't treat astigmatism," he said. "If you ask them how much astigmatism to treat, how much is clinically signifi- cant, almost all of them would say any amount. But with cataract sur- gery, there are still a lot of surgeons who say less than a diopter is not clinically significant." The femtosecond technique Technically speaking, the femtosec- ond laser does not make an LRI, it makes an arcuate incision. To use this technique with the femtosecond laser for cataract surgery, the first step is to take a pre-op topography and a manual keratometry, followed by a keratometry using, for example, an IOLMaster (Carl Zeiss Meditec, Dublin, Calif.). After the readings are collected, they are put into an LRI calculator such as www. lricalculator.com (Abbott Medical Optics, AMO, Santa Ana, Calif.), which tells the surgeon how much cylinder to treat. "We then take the Eric Donnenfeld nomogram and reduce it by one third because these inci- sions are more central and therefore more effective," Dr. Donnenfeld ex- plained. "That tells us exactly where to place the incisions and how long they should be." Surgeons bring that information into the OR and plug it into the femtosecond laser, which allows them to input the length of the inci- sion and its axis, as well as select be- tween one and two incisions. "We then do an intraoperative OCT that shows us the corneal thickness in the area of the inci- sions, and then we adjust the inci- sion to 85% depth. The 85% depth gives us a reproducible result. When we're doing the cataract surgery, we open the incision with a Sinskey hook," Dr. Donnenfeld said. As Dr. Solomon pointed out, though, the incision doesn't have to be opened at the time of surgery. When combined with toric IOLs, the arcuate incisions are created but not opened. There is some variability in keratometry measurements between devices (IOLMaster, topography, auto Ks, manual Ks). Which device is correct? If post-op Dr. Solomon has found that the measurements that were used for toric IOL calcula- tions were correct and the chosen IOL has reduced the residual astig- matism to less than half to a quarter diopter, he doesn't open the arcs. "But if I have more than half a diopter of residual astigmatism in the same meridian, then I have arcu- ate incisions already created that haven't been opened, so the full ef- fect hasn't been realized," he ex- plained. "I can open these with a slit lamp a week to months later. It's something we've been doing with both toric lenses and presbyopia- correcting lenses."

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