EyeWorld Asia-Pacific December 2012 Issue

26 EWAP CATARACT/IOL December 2012 cataract, and visual quality/post-op patient satisfaction is starting to be better understood. Linking pre-op HOAs to post-op satisfaction It wasn’t until Dr. Michelson began taking topography on every cataract patient that the idea gelled about the relationship between pre- op higher order aberrations (HOAs) and post-op satisfaction. “Most of the eye’s higher order aberrations are generally derived from the cornea, while the whole eye’s wave is a composite of the impact of the front and back surface of the cornea and the crystalline lens,” said Jay Pepose, MD , founder and medical director, Pepose Vision Institute, Chesterfield, Mo., USA, and professor of clinical ophthalmology, Washington University School of Medicine, St. Louis, Mo., USA. “Creating corneal incisions and implanting an IOL may radically change the whole eye wavefront and the interaction of the corneal and lenticular components, requiring a period of neural adaptation for the patient,” he said. “We see how patients may need a period of adjustment after implantation of a toric IOL, for example. However, multifocal IOLs implanted in eyes with highly aberrated, irregular corneas may result in reduced contrast sensitivity and poor image quality that may preclude successful neural adaptation.” Without screening for large amounts of higher order corneal aberrations by use of topography, “we cannot scientifically guide the class of IOL selection, and in some patients this may result in a lower quality of vision,” Dr. Pepose said. Dr. Pepose said evaluating HOAs pre-op not only helps determine what type of lens is the best option but will also help identify those who are generally less likely to have optimal quality of vision post-op. “If they’re highly aberrated and show high degrees of asymmetry, we need to convey realistic expectations to patients about the post-op quality or even suggest that they might consider the use of a rigid gas permeable contact lens post-op to optimize contrast,” he said. Even patients who opt for a standard lens will have a lower post-op visual quality if the pre- op corneal wavefronts are highly aberrated, he said. For Dr. Pepose, he disqualifies any patient from multifocal implantation if the cornea is highly aberrated with either vertical or horizontal coma more than 0.3 microns at a 6-mm optical zone. Because the Crystalens AO (Bausch + Lomb, B+L, Rochester, NY, USA) “is aberration-free and does not split light between multiple foci or lose light to useless foci, it therefore does not impact the eye’s wave in the same way a multifocal lens might,” Dr. Pepose said. “I have a lower threshold for Crystalens implantation in these patients with more irregular corneas.” In Dr. Michelson’s study, a retrospective review of 35 patients who underwent an IOL exchange for severe visual dysphotopsia and subsequent multifocal IOL explantation had corneal wavefronts compared to 55 eyes that were tolerant of multifocal lenses. (All wavefronts were captured with Carl Zeiss Meditec [Jena, Germany] Atlas 9000 corneal topography and were computed at 6 mm.) All the HOAs were higher in the dissatisfied group than in the control group, he said. “We looked at all combinations of Zernikes,” he said. “In a nutshell, we found mean RMS values of the combined Z3 and Z4 Zernike aberrations for people who tolerate multifocal lenses to be 0.18 microns; mean values for those who did not tolerate the lens was 0.23 microns.” He called eyes that fall between those ranges to be in the “gray area,” where some are just as likely to be satisfied as dissatisfied. Dr. Pepose said a simple way to understand the importance of HOAs is that each of the polynomial equations mathematically describes a different component of the shape of the wavefront, which are then mathematically combined to describe the entire three- dimensional shape. The second order Zernike describes astigmatism and defocus, while the 3rd order describes coma and trefoil, he said. “When you examine the Zernike pyramid, anything that’s in the center will generally have a far more negative impact on visual imaging than those on the periphery,” Dr. Pepose said. “Coma is in the center, so for me, that’s much more visually significant than if the patient has trefoil, for example.” Dr. Michelson added a second study he co-authored with Rory A. Myer, MD , found that “preoperative topography may be able to predict a patient’s ability to pseudoaccommodate with an aspheric lens.” For practices without a topography instrument capable of deriving a corneal wavefront, Dr. Pepose suggested the VOL-Pro (Sarver & Associates, Carbondale, Ill., USA), a software program that can be used to convert the topographic information from any topography system into corneal wavefront data. “The software lets you input data from any topographer and then constructs a corneal wavefront map for you,” Dr. Pepose said, adding he has no financial interests in the program. The bottom line? “We can now have a higher level of confidence about which patients are going to be satisfied with a multifocal lens,” Dr. Michelson said. “And that, in turn, reduces patient dissatisfaction levels as well as chair time.” EWAP References 1. Michelson MA, Myers RA. Corneal Higher Order Aberrations and Visual Dysfunction With Multifocal IOLs. Paper presented at: American Society of Cataract & Refractive Surgery. 2012: Chicago. 2. Rocha KM, Nose W, Bottos K, Bottos J, Morimoto L, Soriano E. Higher- order aberrations of age-related cataract. J Cataract Refract Surg. 2007;33(8):1442-6. 3. Tong N, He JC, Lu F, Wang Q, Qu J, Zhao YE. Changes in corneal wavefront aberrations in microincision and small- incision cataract surgery. J Cataract Refract Surg. 2008;34:2085-90. 4. Varavka A, Kachanov A, Nikulin S, Chruakov T. Clinical aberrometry and lens pathology. Paper presented at: European Society of Cataract & Refractive Surgeons. 2012: Milan. Editors’ note: Dr. Michelson has financial interests with Alcon (Fort Worth, Texas, USA/Hünenberg, Switzerland) and Oculus (Lynnwood, Wash., USA). Dr. Pepose has financial interests with Abbott Medical Optics (Santa Ana, Calif., USA) and B+L Contact information Michelson: 205-969-8100, mmichel325@aol.com Pepose: 636-728-0111, jpepose@peposevision.com Linking - from page 25