EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/78716
62 EW CATARACT March 2012 IOL range for correcting spherical aberration remains narrow by Matt Young EyeWorld Contributing Editor Customizing spherical aberration correction may be technically challenging, but is the current correction range good enough? I OLs correct a wide range of myopia, hyperopia, and in- creasingly, astigmatism. How- ever, the lenses that correct for spherical aberration—aspheric IOLs—do so in a fixed manner. Each lens manufacturer only corrects for a fixed amount of spherical aberra- tion. There's no customizing this yet. EyeWorld spoke with cataract surgeons well versed in aspheric IOLs to understand more about how lens manufacturers came up with the broad spherical aberration cor- rection amounts, whether lenses should be more customizable to cor- rect varying amounts in the future, and how that might actually hap- pen. Options fixed "After myopia, hyperopia, and astig- matism, it's spherical aberration," said Neil J. Friedman, M.D., adjunct clinical associate professor, Stanford University School of Medicine, Calif., listing the order of impor- tance of visual aberrations needing correction at the time of cataract surgery. Currently, ophthalmologists have limited aspheric IOL choices. Some of these include: • The Tecnis Aspheric IOL (Abbott Medical Optics, AMO, Santa Ana, Calif.), which provides 0.27 microns of negative spherical aberration; • The AcrySof IQ (Alcon, Fort Pediatric continued from page 59 "In other words, I do axial length measurements each year, and the eye becomes slowly more my- opic, so we're managing increasing myopia instead of decreasing hyper- opia. That's less amblyogenic. Their world is near, so they can tolerate mild to moderate myopia," he said. In these cases, he will use a sin- gle-piece acrylic IOL in the bag and a three-piece in the sulcus. EW Editors' note: Dr. Lambert is chair of the Infant Aphakia Treatment Study group and has financial interests with Alcon (Fort Worth, Texas) and Bausch + Lomb (Rochester, N.Y.). Drs. Levin and Medow have no financial interests related to this article. Dr. Wilson is on the steering committee for the Infant Aphakia Treatment Study group and has financial interests with Alcon and Bausch + Lomb. Contact information Lambert: 404-778-3709, slamber@emory.edu Levin: 267-528-9764, alevin@willseye.org Medow: 718-920-6178, nmedow@montefiore.org Wilson: 843-792-7622, wilsonme@musc.edu Worth, Texas), which provides 0.2 microns of negative spherical aberration; and • The Akreos AO (Bausch + Lomb, Rochester, N.Y.), which is spherical aberration neutral. "You have to take two steps back and figure out why they're doing this," said George H.H. Beiko, M.D., assistant clinical professor of ophthalmology, McMaster University, St. Catharines, Ontario. "There's very good evi- dence that it's important not to in- troduce spherical aberration at the time of cataract surgery to improve quality of vision." Dr. Beiko explained that spheri- cal aberration comes from the cornea and the lens. The corneal spherical aberration, which has a positive value, is constant through- out life, with only very minor changes, he said. Lens spherical aberration is very different. It goes from having nega- tive spherical aberration to having positive spherical aberration during one's life, he said. "The initial lenses we placed in people's eyes all had pretty much positive spherical aberration," Dr. Beiko said. "People were getting 20/25—even 20/20 vision—but weren't improving their contrast sensitivity." Researchers realized that the positive spherical aberration in the lens was adding to the positive spherical aberration of the cornea, which detracted from quality of vision. By innovating with aspheric IOLs, they eliminated the positive spherical aberration of the lens and in some cases used negative spheri- cal aberration. It was a turning point for qual- ity of vision, but more advancement may yet be needed. Aspheric IOL manufacturers each have their reasons for inducing negative spherical aberration, or in some cases, being spherical aberra- tion neutral. But the fact is, each as- pheric lens type only gives one option of spherical aberration cor- rection. The "AcrySof IQ Aspheric IOL was engineered with a negative spherical aberration to compensate for the positive aberration of an av- erage cornea," according to Alcon's website. That's for an average cornea—but what about the rest? According to AMO's website: "Wavefront aberration analysis con- firms that the average cornea of a cataract patient has +0.27 microns of spherical aberration throughout life. The Tecnis IOL corrects for –0.27 microns of spherical aberra- tion, just like the average crystalline lens did between the ages of 19-25." So similarly, the Tecnis technology is based on averages. According to Bausch + Lomb's website, the "Akreos AO lens is the world's first aspheric acrylic IOL with aberration neutrality, because the aberrations present in the eye differ from person to person." It's good that Bausch + Lomb recognizes that aberrations differ depending on the individual, but the technology is still spherical aberration neutral. That means there is only one spheri- cal aberration option, not cus- tomized ones. "I don't see a lot of companies investing [in customized spherical aberration correction]," said Dr. Friedman. Nonetheless, there are outliers— people who don't have the average amounts of spherical aberration, he said. The aspheric Tecnis Multifocal IOL Source: Abbott Medical Optics The AcrySof IQ Source: Alcon