EyeWorld Asia-Pacific December 2011 Issue

December 2011 17 EW FEATURE Boris MALYUGIN, MD Chief, Department of Cataract and Implant Surgery Deputy Director General, S. Fyodorov Eye Microsurgery Complex State Institution, Moscow, Russia boris.malyugin@gmail.com M y post-op astigmatic target varies depending on the type of implant used. In monofocal lenses I prefer leaving the patient with 0.5 D of with-the-rule (WTR) astigmatism, while in multifocal the sweet point is between zero and a quarter diopter WTR. During the last couple of years my personal approach to astigmatism correction has undergone substantial evolution. About 5 to 6 years ago, a 2.75-mm clear corneal cataract incision was my first choice. This type of incision is astigmatically active, so it was essential to pay special attention to the meridian of the incision placement. The typical approach at that time was to place the incision at the strongest corneal meridian. In patients with spherical corneas and against-the-rule astigmatism, I was considering temporal incision location. Vector analysis performed at that time revealed a very interesting fact. In spite of the same width of the incision, astigmatic effect was variable depending on the meridian. If placed in the strong corneal meridian, a 2.75-mm incision produced approximately 0.65 D of astigmatism; when positioned in the weak meridian, surgically induced astigmatism was 20% less. Since then, I always take this equation into consideration during the pre-op decision-making process. Summarizing my approach at that time, in most cases astigmatism was corrected with the help of the main incision placement, while in patients with more significant corneal asphericity, limbal relaxing incisions (LRIs) were used. Since then I have moved to microincisional cataract surgery, or MICS, and currently I perform 1.8 coaxial MICS in almost 100% of my routine cases. After switching to MICS and going into the sub-2.0 mm zone, my ability to modify the corneal curvature by selective playing with the position of the main incision significantly decreased. I cannot say that my LRI numbers significantly increased. This is because of the toric lenses introduced into clinical practice. My current approach is to utilize the LRI in cases up to 1.5 D of astigmatism. Patients with more significant astigmatic error are scheduled for the toric implant. I am currently looking forward to the industry providing me with the toric MICS IOL version to be used through a 1.8 mm or smaller incision, which will be a great addition to my surgical armamentarium. Editors’ note: Dr. Malyugin declared no financial interests related to his comments. International point of view Mamalis said. Technical complications such as perforations in the cornea can occur as well, he said. For standard limbal relaxing incisions, most surgeons use either a diamond blade or a metal blade with a preset of approximately 600 microns in depth. These leave quite a bit of leeway in terms of corneal thickness, so for surgeons who are not going to be routinely measuring corneal thickness and then setting their blade accordingly, the risk of a microperforation of the cornea is quite small, Dr. Mamalis said. The most common complication is undercorrection, he said. “We’ll often aim to correct a certain amount of astigmatism and we’ll find that we get 70-80% of it. It’s pretty uncommon to get the full 100%,” he explained. Overcorrection is also a risk, Dr. Devgan said. Diamond, metal, or laser? In terms of blades, Dr. Mamalis said there are some nice metal blades available, but he prefers diamond blades, especially those that are the preset depth and have “little rounded ski tips” on both sides that help to guide the incision. These give a nice, smooth incision and don’t disrupt the corneal epithelium, he explained. Dr. Devgan said both types of blades are effective. Steel blades are the least expensive while diamonds are considered the standard since they tend to be sharper and produce more reliable and consistent incisions, he noted. However, the future may move toward femtosecond lasers for PCRIs since the accuracy is expected to be better, he said. Dr. Mamalis agreed. While he said he doesn’t have experience with the femtosecond laser, he thinks it could potentially be a very accurate way to correct astigmatism because the depth of the incision is controlled by the measurement of the corneal thickness that takes place before the laser is used. But only time will tell. “It’s too early to say if femtosecond lasers will produce better results than diamonds,” Dr. Devgan said. When toric lenses are best Up until a couple of months ago, the toric lenses available in the US were not able to correct high degrees of astigmatism, Dr. Mamalis said. However, the US FDA just approved higher power toric lenses, so surgeons now have the ability to correct a broader range of astigmatism, he said. The lenses that can correct extremely high levels of astigmatism available in Europe have not been approved yet. Toric lenses are great for patients with regular, symmetric, and consistent astigmatism, Dr. Devgan said. “Patients with irregular or asymmetric astigmatism will not do as well with toric IOLs. You can make asymmetric incisions with PCRIs, but toric IOLs are symmetric,” he said. As with PCRIs, Dr. Mamalis said surgeons might want to think twice about implanting toric IOLs in patients with corneal ectatic diseases. In patients with a higher degree of astigmatism, when performing corneal topography, it is important to find out if there’s not only corneal astigmatism but also lenticular astigmatism, he said. “If some of the astigmatism is coming from the lens, you need to take that into account because that’s going to go away when you remove the cataract. You want to make sure you’re calculating the toric lens power on just the corneal astigmatism,” he explained. Similar to PCRIs, the complication with toric lenses is putting them in the wrong axis, Dr. Mamalis said. It’s critical that the toric lens be properly aligned with the axis of the astigmatism. Just like with PCRIs, Dr. Mamalis said he takes the toric IOL calculations with him to the operating room and tapes them above the microscope in the proper orientation to double check the alignment. EW Editors’ note: Dr. Devgan has financial interests with Abbott Medical Optics (AMO, Santa Ana, Calif., USA), Alcon (Fort Worth, Texas, USA/Hünenberg, Switzerland), Bausch & Lomb (Rochester, NY, USA), Haag-Streit (Mason, Ohio, USA), and Hoya (Santa Clara, Calif., USA). Dr. Mamalis has financial interests with AMO, Alcon, and Allergan (Irvine, Calif., USA). Contact information Devgan: 800-337-1969, devgan@gmail.com Mamalis: 801-581-6586, nick.mamalis@hsc.utah.edu