EyeWorld Asia-Pacific December 2011 Issue

December 2011 16 EW FEATURE 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 refractive outcomes. Two approaches, peripheral corneal relaxing incisions (PCRIs) and toric lens implantation, are effective in treating corneal astigmatism and are employed according to the degree of astigmatism. While most surgeons will perform PCRIs when the level of astigmatism is somewhere between 1 D and 1.25 D, some will perform them right down to 0.75 D of astigmatism, said Nick Mamalis, MD, professor of ophthalmology, John A. Moran Eye Center, Department of Ophthalmology & Visual Sciences, University of Utah, Salt Lake City, Utah, USA. Indeed, Uday Devgan, MD, FACS, Devgan Eye Surgery, Los Angeles and Beverly Hills, Calif., USA, 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 completely pressurized and you want to have a totally pressurized, relatively firm eye when you’re doing these incisions. 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 situations where the axis of astigmatism lines up exactly with where the wound is, Dr. Mamalis noted. Surgical challenges for refractive surgeons by Enette Ngoei EyeWorld Contributing Editor “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 astigmatism 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 placement 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 degrees), the patient will now have 1.5 D of corneal astigmatism steep at 90 degrees. So your PCRI must now correct 1.5 D of corneal astigmatism,” 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 diseases, such as keratoconus, performing relaxing incisions will produce unpredictable results, he said. “If there is a condition such as forme fruste keratoconus, which is causing irregular astigmatism, then a PCRI could cause more harm than good and induce further instability into the cornea,” Dr. Devgan said. Low risks Still, the risks of performing PCRIs are few, according to Dr. Mamalis. Putting the incision in the wrong place is one of them. It can be easy to get the axis confused, especially if it’s an oblique axis, he said, so it’s very critical to make sure that those incisions are put in the proper place, otherwise the astigmatism can be made even worse. “What I do, and what I insist that our residents do, is take a picture of the corneal map and the planned area where we’re going to be putting the incisions. I tape that up to the microscope in the operating room and put it in the orientation where we want to make the incision so that there’s no question that we’re putting the incision in the proper place,” Dr. AT A GLANCE • While most surgeons will perform PCRIs when the level of astigmatism 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 femto second lasers for PCRIs since the accuracy is expected to be better • Up to a couple of months ago, the toric lenses available in the US were not able to correct high degrees of astigmatism. However, the US 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 “Toric lenses are great for patients with regular, symmetric, and consistent astigmatism” – Uday Devgan, MD, FACS There are few risks in performing PCRIs, according to Nick Mamalis, MD Source: Uday Devgan, MD, FACS