Eyeworld

EW FEATURE 60 by Enette Ngoei EyeWorld Contributing Editor Astigmatism management: Challenges for refractive surgeons EyeWorld takes a look at two approaches for treating astigmatism M anaging pre-existing corneal astigmatism at the time of cataract surgery is integral to achieving optimal re- fractive outcomes. Two approaches, peripheral corneal relaxing incisions (PCRIs) and toric lens implantation, are effective in treating corneal astig- matism and are employed according to the degree of astigmatism. While most surgeons will per- form PCRIs when the level of astig- matism is somewhere between 1 D and 1.25 D, some will perform them right down to 0.75 D of astigmatism, said Nick Mamalis, M.D., professor of ophthalmology, John A. Moran Eye Center, Department of Ophthal- mology & Visual Sciences, Univer- sity of Utah, Salt Lake City. Indeed, Uday Devgan, M.D., F.A.C.S., Devgan Eye Surgery, Los Angeles and Beverly Hills, Calif., said he performs PCRIs at 0.5-1.0 D of corneal astigmatism. At 1.25 D to 1.5 D, he will either do a PCRI or toric IOL implantation, he said. When to perform PCRIs Dr. Mamalis prefers to perform the PCRIs at the beginning of the cataract surgery. "The reason is the eye is com- pletely pressurized and you want to have a totally pressurized, relatively firm eye when you're doing these in- cisions. Sometimes at the conclusion of the case, the eye is not totally pressurized and it's hard to make sure that you're getting an accurate incision," he explained. There are, however, certain situ- ations where the axis of astigmatism lines up exactly with where the wound is, Dr. Mamalis noted. "I'm not going to make a large relaxing incision right where my wound is going to be; I can't risk that coming open, so I'll make an incision opposite from where my wound is, if that's where the astig- matism is at the beginning of the case. Then at the end of the case, I'll extend where my wound was to give the astigmatism control," he said. On the other hand, Dr. Devgan likes to perform the PCRIs at the end of cataract surgery. The key is that the surgeon must factor in the place- ment and astigmatic effect of his or her cataract incisions with the PCRIs. "For example, if the patient has 1 D of corneal astigmatism steep at 90 degrees and then you place a phaco incision at 180 degrees (the phaco incision will cause about 0.5 D of corneal flattening at 180 de- grees), the patient will now have 1.5 February 2011 Challenging refractive cases October 2011 Slug: COV4_1011_astigmatism Word count: 1530 Images: 2 AT A GLANCE • While most surgeons will perform PCRIs when the level of astigma- tism is somewhere between 1-1.25 D, some will perform them right down to 0.75 D of astigmatism • The surgeon must factor in the placement and astigmatic effect of his cataract incisions with PCRIs • Surgeons should avoid doing PCRIs whenever there is a question of either corneal disease or irregular astigmatism • 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. However, the future may move toward fem- tosecond lasers for PCRIs since the accuracy is expected to be better • Up to a couple of months ago, the toric lenses available in the U.S. were not able to correct high degrees of astigmatism. However, the U.S. FDA just approved higher power toric lenses so surgeons now have the ability to correct a broader range of astigmatism. The lenses that can correct extremely high levels of astigmatism available in Europe have not been approved yet continued on page 62 International point of view Moscow, Russia 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 quar- ter diopter WTR. During the last couple of years my per- sonal approach to astigmatism correction has undergone substantial evolution. About 5 to 6 years ago, a 2.75-mm clear corneal cataract inci- sion was my first choice. This type of incision is astigmatically ac- tive, 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 inci- sion location. Vector analysis performed at that time revealed a very interest- ing 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 astigma- tism 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 micro-incisional 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 selec- tive 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 astig- matism. Patients with more significant astigmatic error are sched- uled 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 arma- mentarium. Contact information Malyugin: boris.malyugin@gmail.com D of corneal astigmatism steep at 90 degrees. So your PCRI must now correct 1.5 D of corneal astigma- tism," he explained. Surgeons should avoid doing PCRIs whenever there is a question of either corneal disease or irregular astigmatism, Dr. Mamalis said. In eyes with progressive ectatic dis- eases, such as keratoconus, perform- ing relaxing incisions will produce unpredictable results, he said. "If there is a condition such as Boris Malyugin, M.D. 52-67 Feature_EW October 2011-DL33_Layout 1 9/29/11 4:51 PM Page 60

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