Eyeworld Supplements

Roundtable discussion: Choices in clinical practice subtle contribution to visual quality, but added together they make for a perceptibly better visual outcome. Dr. Chang: I agree that there is a syner- gistic effect. But if I have to split hairs, my personal opinion is that CA is likely even more significant than SA. SA is a surface curvature property, so the ability of an IOL to minimize SA of the entire eye depends on the specific SA of the cor- nea. CA is a material-dependent property that benefits every eye. Cataract surgery with an IOL with an Abbe number great- er than that of the natural lens (47) can improve CA, so that our cataract patients could actually experience better vision quality than they did as young adults. Dr. Chang: Let's talk about spherical aberration. Is it an advantage to leave some SA to increase depth of focus? Dr. Garg: Hoya has an IOL that provides greater depth of focus through positive SA. That could be an advantage in terms of the flexibility of vision, but not in sharpness of vision. Dr. Ma: An SA-induced increase in depth of field comes with a compromise in contrast sensitivity. In laser vision correc- tion our goal has always been to achieve "super vision," so it's interesting that in cataract surgery we're talking about how much compromise people can tolerate. All things being equal, I'd rather not compromise on image quality if I don't have to. Dr. Chang: For a patient who frequent- ly drives at night, what optical consid- erations are important? Dr. Wörtz: I believe you need to edu- cate all patients about the potential for pseudophakic visual phenomena, which can include dysphotopsias, glare, and halos. Most patients have an easier time adapting to these symptoms if they understand that they are not out of the ordinary and are educated preoperatively about them. Also, aspheric optics tend to make a difference in night-time driving Gary Wörtz, MD: I agree. When you implant a multifocal lens, it is essential to get everything else—material, capsu- lorhexis, centration, and ocular surface— right. If you are going to split incoming light rays for multifocal vision, you definitely want that light to be in crisp focus, with as little spherical and chro- matic aberration as possible. Dr. Chang: I agree. In addition to what we as surgeons can do to optimize visual quality, it is important for IOL manufac- turers to balance the optical properties of refractive index, spherical aberration, and chromatic aberration to give us lens- es that provide maximal image quality with as much forgiveness as possible. Dr. Chang: Do you think spherical aberration (SA) or chromatic aberra- tion (CA) is more important for optical quality? Dr. Wörtz: SA has gotten more attention in the past but that may only be because it was an easier problem to solve with design modifications. CA is an optical property that is more material-related and harder to change. I think CA gets downplayed but it is really important. Joseph Ma, MD: Do we have to choose? They are both important for high quality vision; how one might rank them might be patient and task dependent. For ex- ample, for most patients, night myopia from CA may be more important than SA for driving at night, while optimiz- ing SA may have more effect on reading depending on that particular patient's amount of corneal SA. There are lenses and laser algorithms that attempt to increase effective depth of field and in- termediate reading by inducing more SA than normal. On the other hand, we will also soon have a lens that uses chromatic aberration to help achieve improved contrast in a diffractive lens design. Dr. Garg: To me, it's really the summa- tion of SA and CA, along with other optical qualities, that is more important. Taken on its own, each one makes a Daniel Chang, MD (moderator): As you all know, optics is something I'm passionate about. What are the optical principles that are important to you in evaluating new IOLs? Jeremy Kieval, MD: Spherical aberration correction is very important. I'm starting to look at the role of correction of chro- matic aberration, too, so I look for infor- mation about the lens material's Abbe number and index of refraction. The potential for glistenings is something I keep in mind, although I'm still waiting for data on whether glistenings truly compromise image quality. Sam Garg, MD: I want to know that the manufacturing of the lenses is done within very tight parameters so I can feel confident that the optical results are reproducible. When I'm considering any new entrant to the market, I expect it to be at least on par with current IOLs and, ideally, a step better. I match my spherical aberration (SA) to the patient so that I get SA close to zero. My goal is to give patients vision that is as close as possible to what they had at age 20, or even better. Dr. Chang: What have we learned about optical quality from experiences with multifocal IOLs? Dr. Kieval: Multifocal IOLs are phenom- enal devices with many advantages for our patients but, by virtue of the optical principles that provide multifocality, they do reduce image quality. That has forced all of us to work harder to control factors such as residual refractive error, dry eye, and higher-order aberrations that can otherwise compound the reduc- tion in contrast sensitivity and image quality with multifocal IOLs. Dr. Garg: I see a fair number of multi- focal IOL patients for second opinions. In the vast majority of cases, everything went right with the surgery, but the patient is bothered by the quality of vision, either because their expectations were not set appropriately or their ocular surface issues are not being addressed. 6

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