EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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40 EW CATARACT September 2012 Cataract editor's corner of the world Linking pre-op HOAs to post-op satisfaction rates by Michelle Dalton EyeWorld Contributing Writer P resbyopia correction is often considered the "holy grail" in cataract surgery. Refractive IOLs have been created to achieve this elusive goal. While the currently available presbyopia-correcting IOLs do often deliver satisfactory outcomes, they can also have concomitant visual disturbances. Cataract surgeons have been seeking pre-op tests that can predict levels of patient satisfaction. Recently, researchers have found a correlation between higher order aberrations (HOA) and acceptance of visual outcomes. Understanding and quantifying variables, such as HOAs, may lead to better screening of patients and ultimately to customization of the IOL choice. Bonnie An Henderson, M.D., cataract editor New data suggests that 3rd and 4th order Zernike terms are most likely to in- fluence patient satisfaction with premium lenses T he higher the pre-op root mean square (RMS) value for combined 3rd and 4th order Zernike terms, the greater the intolerance for multifocal lenses will be, according to a paper presented at this year's ASCRS•ASOA Symposium & Congress.1 reduction of optical quality, he said, and 25% of patients who have mul- tifocal lenses report some degree of dysphotopsia. In 2007, Rocha et al.2 found different types of lenticular opacities induce different wavefront aberration profiles, and in 2008, Tong et al.3 found changes in These findings may help explain why one group of patients does well with multifocal lenses but another group does not, the study authors say, and lends credence to the argument that every cataract patient should undergo a wavefront analysis. According to Marc Michelson, M.D., associate clinical professor of ophthalmology, University of Alabama School of Medicine, Birmingham, and in private practice, Michelson Laser Vision Inc., Birmingham, and Alabama Eye & Cataract Center, Birmingham, "there is a significant degree of dis- satisfaction among people who get premium lenses, and surgeons im- plant these lenses without knowing who is tolerant and who may not be." Light scatter can lead to a corneal wavefront aberrations were dependent upon incision size, with micro-incisions minimizing the effect on optical quality when compared to small incision cataract surgery. And at this year's ESCRS meeting in Milan, Varavka et al.4 will present their study findings on coma and lens dislocation. Dr. Michelson said the relationship between aberrations, 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 im- pact of the front and back surface of the cornea and the crystalline lens," said Jay Pepose, M.D., founder and medical director, Pepose Vision Institute, Chesterfield, Mo., and professor of clinical ophthalmology, Washington University School of Medicine, St. Louis. "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 Combined Zernike 3rd and 4th order aberrations will help determine who is most likely to be dissatisfied with a multifocal IOL Source: Marc Michelson, M.D. 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 con- sider 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 implan- tation 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, N.Y.) "is aber- ration-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 thresh- old for Crystalens implantation in these patients with more irregular corneas." In Dr. Michelson's study, a retro- spective review of 35 patients who underwent an IOL exchange for severe visual dysphotopsia and sub- sequent multifocal IOL explantation had corneal wavefronts compared to 55 eyes that were tolerant of multi- focal 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 aberra- tions 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