Every year, Cataract & Refractive Surgery Today Europe and Cataract & Refractive Surgery Today convene a roundtable of opinion leaders on IOLs without any sponsorship from industry. Our goal is to discuss controversial topics with surgeons who have differing opinions and experiences. This year, we invited several leading refractive IOL surgeons to talk about what is new and different in their practices.
CURRENT PRACTICE
Chang: As has been the case for the past several years, presbyopia-correcting IOLs are the foremost topic on every cataract and refractive surgeon's mind. Let me begin by asking everyone to summarize his current preferences with these IOLs.
Pepose: My practice is mostly cornea, cataract, and refractive surgery. I prefer accommodating lenses, but sometimes I will mix IOL types.
Knorz: I offer refractive surgery, both corneal and intraocular. My patients receive phakic IOLs or undergo refractive lens exchange, for which my standard protocol is to mix lenses. I am using the ReZoom Multifocal IOL (Advanced Medical Optics, Inc., Santa Ana, California) predominantly and the Tecnis Multifocal IOL (Advanced Medical Optics, Inc.).
Hardten: My practice is a combination of cornea; refractive surgery, including LASIK and PRK; and cataract/IOL surgery. I perform probably 10% refractive lens exchange and 90% cataract surgery. I use all of the presbyopia-correcting lenses that are available in the United States, and I mix them occasionally. In general, however, I implant the ReZoom IOL bilaterally when the patient does well with the ReZoom lens in his first eye.
Pietrini: I am a refractive corneal and cataract surgeon. My approach for correcting presbyopia began with corneal presby-LASIK in hyperopes, but I extended to refractive lens exchange approximately 3 years ago, with the development of new diffractive optics such as the Acri.Tec Acri.LISA (Carl Zeiss Meditec AG, Jena, Germany). I had the opportunity to evaluate the Acri.LISA in France 2 years ago. My experience with multifocal IOLs began with the Array (no longer available; Advanced Medical Optics, Inc.) and the ReZoom. But, I rapidly switched to diffractive optics with the Restor (Alcon Laboratories, Inc., Fort Worth, Texas) and Acri.Tec multifocal IOLs (Carl Zeiss Meditec AG). In my current practice, I implant the Acri.LISA in both eyes for refractive lens exchange and cataract surgery.
Donnenfeld: I am a cornea-trained ophthalmologist and a comprehensive anterior segment surgeon whose real interest is refractive corneal and cataract surgery. I perform LASIK a little more frequently than I do cataract surgery, but I have become excited by refractive IOL surgery. I have been involved in several clinical trials. I use all three of the refractive IOLs available in the United States, and I had a good experience with the Tecnis IOL (Advanced Medical Optics, Inc.) during its clinical trials. I continue to mix lenses most of the time based on my patients' experiences.
Claoué: I specialize in advanced cataract surgery techniques, refractive surgery with a special interest in presbyopia correction, and corneal transplant surgery. I work in the NHS state hospital system and am in independent practice.
I first described what is now called PRELEX (an acronym for presbyopic lens exchange, as coined by Dr. Kevin L. Waltz, MD, OD) in 1997, when, at the European Society of Cataract and Refractive Surgery (ESCRS), I reported a hyperopic patient who underwent a refractive lens exchange with a foldable multifocal IOL in order not to wear spectacles for distance or near vision. Although I was criticized at the time, history has proved that not only is this technology effective and viable, but that to date we have nothing as predictable as refractive multifocal IOLs to achieve presbyopia correction.
Chang: I am predominantly a cataract and IOL surgeon. Like Eric, I use the AcrySof Restor IOL (Alcon Laboratories, Inc.), the Crystalens (Eyeonics, Inc., Aliso Viejo, California), and the ReZoom IOL regularly, mostly with matching but occasionally with mixing.
Rau: I have been implanting the Akkommodative 1CU (HumanOptics AG, Erlangen, Germany) since 2003. For presbyopia correction, I implant this lens in the dominant eye of patients who complain about glare. I use it in combination with a diffractive IOL in the nondominant eye.
DEVELOPMENTS IN 2007
Crystalens Five-O
Chang: Several new modifications to presbyopia-correcting IOLs were introduced in 2007. Jay, how does the Crystalens Five-O differ from the earlier 4.5 model?
Pepose: There were a number of changes, the most obvious of which is that the optic is now 5 mm instead of 4.5 mm (Table 1). There is more adherence between the haptics and the capsule with the new model as well. The Five-O design was based on some of the initial prototypes by J. Stuart Cumming, MD, that showed the greatest movement of the plate by the creation of a uniform, rectangular pocket in the capsular bag, which promotes sliding during accommodation. The newly fashioned haptic plates and loops provide additional capsular-bag support and excellent optic centration. The haptics of the Crystalens Five-O are designed to fold inward toward the optic, thus facilitating their folding in an insertion device.
I think the new design achieves superior refractive outcomes in terms of distance correction. I also find that the amount of vaulting is more consistent. The improved predictability is due, in part, to greater surface-area contact between the plates and the capsule. This greater consistency in the estimated lens position is also a reflection of the lens' coming in an 11.5-mm diameter for IOLs greater than 19.00 D and a 12-mm overall diameter for dioptric powers of up to 19.00 D, because more myopic patients tend to have larger eyes and capsular bags. There is a difference in the A-constant in this lens in comparison to the Crystalens 4.5 that reflects a different degree of posterior-optic vaulting. In my experience, patients have somewhat better near vision with the Five-O than the Crystalens 4.5.
Donnenfeld: For me, the biggest advantage of the Five-O over the 4.5 is that I have fewer complications after the perfect insertion of the lens. My biggest complaints with the 4.5 were z syndromes, decentrations, and a lot of refractive instability. My enhancement rate with the Crystalens was exorbitantly higher than with multifocal IOLs. My enhancement rate continues to be higher with the Crystalens due to refractive uncertainty, because the lens moves in the capsular bag, but it is now maybe 50% versus three times higher than with the other IOLs.
I am not certain if my patients are better able to read with the Crystalens Five-O. I think that their distance visual acuity is better with the larger optic. I have had no cases in which the IOL migrated.
Hardten: My biggest frustration with the Crystalens 4.5 was the z syndrome, which I have not observed with the Five-O. The new lens also seems to sit more evenly in the capsular bag. I think the sizing of the anterior capsulorrhexis and the capsular bag is more forgiving with the Five-O, and glare and halos at nighttime seem to be less of an issue. Although the Crystalens 4.5 sat fairly far posteriorly, my patients generally had a similar level of glare and halos as with the multifocal IOLs. Unwanted visual phenomena do not seem to be as much of an issue with the Five-O.
Chang: With the Crystalens 4.5, I think many of us were surprised at our inability to achieve emmetropia as predictably as we could with other IOLs. The likely reasons for this make sense: The axial position of a hinged optic is going to vary depending upon the size of the bag and capsulorrhexis. Personalizing your A-constant improves your average but does not reduce the standard deviation. The larger optic, the broader haptics, and the greater overall length of the Crystalens Five-O for lower powers have improved this platform's refractive predictability in terms of a tighter standard deviation around the refractive target.
Knorz: In Europe, studies are showing there is virtually no movement of the so-called accommodating lenses.1 The perception is that, if an accommodating lens does not move, it does not work. I am not using the Crystalens.
Chang: Do we understand the mechanism of the accommodative or pseudoaccommodative effect any better?
Claoué: The short answer has to be, not at all. We still have problems trying to understand how accommodative IOLs work—if at all—as conflicting data is vociferously presented, often by parties with vested interests. Until this physiology is better documented and understood, the proven optical solution of multifocal IOLs remains the gold standard.
Pepose: We do not fully understand the mechanisms that may underlie patients' improved near and intermediate vision with this lens design, and they are likely to be multifactorial. If the sole mechanism were anterior movement of the optic, then you would expect a higher dioptric lens power to produce a greater accommodative effect. I do not think any studies support this relationship between IOL power and near vision with the Crystalens. I therefore think it is probably a combination of pseudoaccommodation due to the posteriorly vaulted optic's being closer to the nodal point of the eye along with changes in the optic's shape and axial movement. The change in the optic's shape may produce a central power gradient in the lens, and this phenomenon (observed during accommodation of the crystalline lens) has been referred to as accommodative arching.
Donnenfeld: Surgeons' adoption rate of refractive IOLs has not been high, perhaps because the refractive outcomes must be extraordinarily precise to satisfy patients. The advantage of aspheric optics is a wider sweet spot. Patients who receive the AcrySof Restor Aspheric IOL or the Tecnis Multifocal lens do not require a plano or 0.25 D result to be very happy.
Pietrini: The development of aspheric IOLs is one of the most important progressions in multifocal optics because of the resulting improvement in quality of vision. It is the reason why all companies have added an aspheric component onto the optic of multifocal IOLs, which is crucial for the quality of vision in low-light conditions. Contrast sensitivity is much better with an aspheric IOL, because the IOL not only corrects sphere and presbyopia, but also spherical aberration. Moreover, there is no variation of the refraction with pupil dilation, and this phenomenon contributes to better vision and a reduction of halos. Since we use aspheric IOLs, only a few of our patients have significant halos.
Knorz: My experience is mostly with the Tecnis Multifocal lens. Both spherical and multifocal IOLs are associated with halos at night. An aspheric optic does eliminate some of the halos, which are the most significant side effect of multifocal IOLs. Asphericity is therefore an advantage in a multifocal IOL.
Donnenfeld: I think I agree. Halos and glare are reduced. Their biggest cause is not asphericity, however, but refractive defocus. If you can eliminate the higher-order aberration, you have a little more wiggle room in terms of defocus.
Pietrini: Another advantage of asphericity is a better tolerance of the IOL to small refractive errors because of the defocus curve and to small amounts of cylinder.
Chang: Some surgeons mention their impression that the aspheric optic improves near performance, but the aspheric surface really affects the periphery of the IOL's optic and not its center.
Donnenfeld: That would be unexpected. Less spherical aberration means less depth of field with sharper vision at the desired focal distance. I have been happy with my patients' near vision after receiving the AcrySof Restor Aspheric IOL; they have a crisp view at the 4.00 D reading add.
Rau: Some patients implanted with the Restor complain about reading difficulties on the computer, as they find it necessary to hold text very near to their eyes. I do prefer to implant the Restor in patients with discrete changes in the macula, however, due to the IOL's blue filter. These patients often wish to become spectacle independent. The distance vision is good with the Restor Aspheric, and the near vision is excellent.
Donnenfeld: What about midrange vision, however, where depth of field is really the issue? The Crystalens has positive spherical aberration, which slightly decreases quality of vision at distance but gives greater depth of field for more midrange vision. Eliminating spherical aberration may compromise midrange visual acuity.
Knorz: We need more clinical data to prove that asphericity increases depth of field. It is counterintuitive.
I conducted a prospective, randomized, masked comparison of the Acrysof Restor and the Tecnis IOLs.2 Both lenses were implanted bilaterally, and my colleagues and I initially found that they were similar in terms of contrast sensitivity and distance vision. The differences we observed related to visual acuity at near and in dim light, as one would expect due to the smaller optical zone of the AcrySof Restor lens. Additionally, we found that patients' reading speed was significantly higher even in bright light with the Tecnis Multifocal lens than with the AcrySof Restor IOL.
Chang: To what do you attribute the difference in the two groups' ability to read in bright light?
Knorz: I do not know. My colleagues and I did not observe a significant difference in contrast sensitivity between the groups, even in low light, which was another unexpected finding. We anticipated that the Tecnis Multifocal IOL would perform better because of its asphericity. On the other hand, the AcrySof Restor lens has no near add in the periphery, which allows it to perform better in dim light. Perhaps these qualities balanced each other. The results of our study demonstrate that surgeons should not base their choice of IOLs on their theoretical performance. They need clinical data.
Claoué: Given that one of the theoretical problems with multifocal IOLs is the loss of contrast sensitivity that can be measured in an optical lab, the abolition of spherical aberration is a logical step to maximize the use of light for visable images. I use these terms explicitly, as we must remember that in addition to splitting light into visable images (for distant and near objects), the physical optics of diffractive lenses means that up to 20% of the incident light is diffracted into higher-order images that can never be visualized (ie, wasted). To me, this makes no sense: All available light should be used for visable images to minimize loss of contrast sensitivity. We tend to forget that the aged macula has a loss of contrast sensitivity related to the aging process, which we cannot influence. It is therefore important to concentrate on optimizing the optics, which we can influence.
Hardten: The point of focus is slightly farther out with the Tecnis Multifocal IOL versus the AcrySof Restor lens. The greater reading speed with the former may be due to the wider field of view. In a sense, patients can look ahead at more words and therefore read even faster. Most people do not read at 12 to 14 inches but at approximately 16 inches when they are trying to read typically sized print quickly as opposed to reading very small print.
Knorz: The patients who received the Tecnis Multifocal lens preferred that their reading material be 2 to 3 cm farther away than did those with the AcrySof Restor lens despite the same near add (the average distance for reading was 35 cm with the Tecnis Multifocal IOL and 32 cm with the AcrySof Restor lens2).
Donnenfeld: Your findings reaffirm my impression of the Tecnis Multifocal lens. The take-home message from your study was that both IOLs produce great outcomes. Patients achieved slightly better reading vision with the Tecnis Multifocal lens, and I have found that clinically as well. The only issue that I think remains to be resolved is which lens provides better distance vision, especially at night.
Knorz: Our study did not show any difference between the Tecnis Multifocal IOL and the AcrySof Restor lens regarding distance vision. When comparing the refractive ReZoom lens with the Tecnis Multifocal IOL or the AcrySof Restor lens, however, patients had one more line of best corrected distance vision with the ReZoom lens, which is distance dominant, than with the Tecnis Multifocal and AcrySof Restor IOLs based on my clinical experience. Most patients tolerate the loss of one line, but some do not, especially in their dominant eye.
Chang: Unlike with the Tecnis Multifocal IOL, the periphery of the AcrySof Restor's optic is purely distance. With large pupils, the Tecnis Multifocal IOL therefore presents many more diffractive rings than the AcrySof Restor lens. Was there a difference in the number of subjective complaints about halos or rings between the two subject groups?
Knorz: Interestingly, there was not. As I said, we found no difference between subject groups in terms of contrast sensitivity, distance vision, glare, and halos in dim light. Maybe the Stiles-Crawford effect is responsible.
Rau: I have been implanting the Tecnis since 2004, and my patients are satisfied with this lens. The Tecnis provides a good distance vision and excellent near vision with fast reading speed. The prolate anterior surface compensates for spherical aberration of the cornea and improves vision in low-light mesopic conditions. Compared with the ReZoom, the near vision of the Tecnis multifocal is even better. The patient need not to hold the text so near. The patient complains less about halos and glare than they do with the Restor or ReZoom.
Claoué: We have had the Tecnis in Europe for some time, and there is no doubt that it works. However, for PRELEX, it is mandatory to have a 360º square edge to minimize posterior capsular opacification (PCO). A PRELEX patient who develops PCO has been given an iatrogenic media opacity, and this is not acceptable. Unfortunately, the Restor has an achilles' heel with the square edge missing at the haptic-optic interface, and this makes it unacceptable to me as an IOL for PRELEX. In contrast, other IOLs such as the ReZoom, Tecnis Multifocal, and the M-Flex (Rayner Intraocular Lenses Ltd., East Sussex, UK) do have a 360º square edge, and with respect to PCO, they are preferable IOLs for PRELEX patients.
WAXY VISION AND HIGHER-ORDER ABERRATIONS
Chang: The quality of vision with diffractive IOLs is highly subjective, but it is a matter of concern for a lot of surgeons. What has your experience been with so-called waxy vision?
Pepose: Some of my patients who have received the AcrySof Restor lens have complained of waxy vision. If you look at the way the AcrySof Restor lens splits light in an eye with a small pupil, there is an energy continuum focusing about 40% of the light at a near focus and about 40% at distance, and you are losing about 20% to higher diffractive orders.
This wasted 20% of light energy is a consequence of the overall interaction of light with the diffractive steps of the AcrySof Restor IOL. With this lens design, it is not possible to direct 50% of the light to each of the two primary foci. There are also a lot of unknowns in terms of the position of the lens in relation to the visual axis. As you start to get more higher-order aberrations, you start to become really sensitive to residual second-order aberrations like defocus and astigmatism, thus increasing the likelihood that laser vision enhancement will be needed.
In our comparative study, my colleagues and I found that the Crystalens was superior to the AcrySof Restor IOL in terms of best corrected distance vision when tested monocularly or binocularly. Regarding uncorrected vision at distance, there was no statistical difference between the Crystalens, ReZoom, and AcrySof Restor lenses3
Hardten: Because waxy vision does not happen frequently, it is not the first problem that you consider when a patient complains. Instead, you go through a long list of possibilities such as ocular dryness, cystoid macular edema (CME), capsular opacity, and residual sphere or cylinder.
Chang: Waxy vision associated with a multifocal IOL is a diagnosis of exclusion, in other words.
Rau: Some of my patients have complained about waxy vision, even when their distance and near vision are 20/20 and the lens is centered. Sometimes, this phenomenon disappears within 1 year.
Pietrini: In my experience, the phenomenon of waxy vision is extremely rare with the Acri.LISA, because the lens has optical properties contributing to a good quality of vision. Its asphericity and correction of aberration lead to a spherical aberration close to zero; there is an asymmetric distribution of light (65% for far, 35% for near); and the very smooth diffractive steps on the optic reduce halos. The Acri.LISA is the first diffractive IOL implantable through a 1.5- to 1.8-mm incision. This very small incision also reduces corneal induced aberrations.
Donnenfeld: Waxy vision definitely exists. It is mostly associated with the AcrySof Restor lens, but I have also encountered it with the ReZoom lens. My colleagues and I have been looking at the effect of the IOL's centration relative to the pupil. The capsular bag does not sit directly behind the pupil, and the difference in location is known as angle kappa. If an IOL is decentered relative to the pupil but is right in the middle of the capsular bag, the resultant higher-order aberrations are going to create waxy vision. Jack Holladay, MD, and I have actually developed some models to study this phenomenon, and we think this scenario explains a lot of the problems with quality of vision that are not correctable through normal means after the implantation of refractive IOLs. By simply performing argon laser iridoplasties to center the iris over the IOL (Figures 1 and 2), we have been able to improve the quality of vision significantly in almost all of these patients and eliminate waxy vision4 (see Argon Laser Iridoplasty for Recentering the Pupil Over an IOL on page 60). One such patient experienced an improvement from 20/40 BCVA to 20/25 UCVA after the procedure.
Chang: Paolo Vinciguerra, MD, used the Nidek OPD Scan (Nidek Co., Gamagori, Japan) to measure the total ocular wavefront in a few patients who were complaining about their quality of vision and in whom the AcrySof Restor lens was decentered relative to the pupil. After he surgically recentered the AcrySof Restor lenses, the measured aberrations and the patients' symptoms improved (see Restor IOL Centration and Optical Wavefront on page 72). Apparently, diffractive optics that are decentered relative to the pupil can induce coma and other higher-order aberrations.
Donnenfeld: More aberration is induced by diffractive than refractive multifocal IOLs. Diffractive lenses split light in a different way than refractive IOLs.
Chang: Based upon Dr. Vinciguerra's recommendations, for the past 2 years, I have positioned the AcrySof Restor lens with its haptics at the 6- and 12-o'clock positions, and I take advantage of the tacky hydrophobic material to slightly nudge the lens a little nasally (Figure 3). This technique has been surprisingly effective for aligning the diffractive optic with the pupil, which is always a bit nasally decentered relative to the capsular bag.
Hardten: I also use wavefront diagnostic testing to capture that limbus-to-pupil relationship. The wavefront provides a really good picture of this relationship.
Donnenfeld: I have a large refractive corneal practice, and I see many patients who have had PRK or LASIK, have developed cataracts, and want to undergo IOL surgery. Early on, I frequently implanted refractive IOLs. I am now more conservative. I will rarely choose a diffractive multifocal IOL for a post-LASIK eye but feel comfortable implanting a refractive multifocal IOL such as the ReZoom. Refractive IOLs perform better in these patients because they induce fewer higher-order aberrations. Alternatively, I implant a Crystalens in these cases when the previous treatment was for high myopia, the cornea is extremely oblate, or the ablation was decentered.
Knorz: Because refractive surgery induces a large number of higher-order aberrations, it does not make sense to implant a multifocal IOL in these eyes.
Chang: Many surgeons perform laser vision enhancement to address the residual refractive error after the implantation of a multifocal IOL in an eye that has undergone myopic LASIK. The point is that a patient might see 20/25 and J2 after an enhancement procedure for his spherical refractive error, but the surgeon really has no idea what the aberrations and the quality of vision are.
Hardten: Another advantage of the refractive IOL in that post-LASIK patient is that you can manipulate the pupil's size postoperatively to reduce visual symptoms or higher-order aberrations, because the center of a refractive IOL is emmetropic.
Chang: To summarize everyone's comments, the term waxy vision describes a variety of conditions that diminish visual quality. Is the problem any less with the Tecnis Multifocal IOL?
Knorz: Substantiating data are needed, but my colleagues and I did not find any difference between the Tecnis Multifocal and the AcrySof Restor lenses in terms of BCVA and UCVA. Both IOLs provide excellent distance and near vision. It is important to remember, however, that all multifocal lenses, especially those with an equal distribution between distance and near vision, require a certain sacrifice, which means that there is a small loss of BCVA compared with a monofocal IOL.
Pepose: Aberrations of the anterior corneal surface are a major component in the degradation of the retinal image, but we do not routinely measure them preoperatively.
Chang: That is a great point, because we all ultimately would like to predict what patients will have problems with their quality of vision with a multifocal IOL.
