Symposium: Wavefront-Designed IOLs: Correcting Corneal Aberration for Safer, Sharper Vision
R. Bruce Wallace III, MD, FACS: Advances in IOL technology are leading ophthalmologists in a new direction for cataract surgery. Ophthalmologists are now focused on providing patients with the best possible quality of vision. Quality vision is more than visual acuity — more than simply being able to read the familiar 20/20 at the bottom of a Snellen Chart (Figure 1).
Choosing the appropriate IOL for each patient is necessary to provide the best outcomes. This panel discussion covers new criteria for selecting IOLs, improving functional vision, current IOL designs, surgical techniques for implanting IOLs and the future of IOL technology.
How do you select the right IOL for your patients?
Samuel Masket, MD: I try to select an IOL that will bring each patient the greatest degree of satisfaction because patients will judge the performance of the surgery based on their resulting quality of vision.
I consider a patient’s lifestyle. Will he or she be driving at night? Will the patient be involved in activities in low lighting conditions? I consider the cosmetic aspects of the surgery, for example, how the lens looks in the eye, and I consider ocular comorbidities, as certain ocular conditions, such as pseudoexfoliation, require use of specific IOLs.
Ulrich Mester, MD: Generally, I prefer third-generation silicone IOLs for all patients except for those with diabetes or high myopia. For these patients, I select acrylic IOLs because of the possible later need for vitreous surgery with silicone oil.
I listen to what the patient wants and determine which IOL fits his or her functional requirements. Functional vision is a measure of how well the IOL allows patients to carry out activities in their daily lives. I also consider the patient’s refraction in the fellow eye.
Masket: Laser refractive surgery has greatly changed our patients’ expectations. With the distinction blurring between cataract and refractive surgery, ophthalmologists must provide IOLs that can match their patients’ visual expectations.
Michael Colvard, MD, FACS: Keratorefractive surgery helped ophthalmologists to understand the importance of visual quality. Laser refractive surgery taught ophthalmologists that it is possible to improve visual acuity and actually diminish visual quality. Ophthalmologists now clearly understand the need to improve both.
For decades, cataract surgeons realized that many patients were still having trouble driving at night, even after “successful” cataract surgery. It is remarkable that it took ophthalmologists so long to understand why. Ophthalmologists are trained in optics and understand the importance of aspheric lens design in reducing spherical aberration. The relationship between spherical aberration and aperture size (pupil size) is well known to every first-year resident in ophthalmology. Yet, inexplicably, ophthalmologists ignored this in clinical practice. Cataract surgeons should have realized the obvious relationship between correction of spherical aberration and improved night vision sooner.
Masket: Ophthalmologists have learned much from unhappy patients after refractive surgery. Patients may achieve 20/15 visual acuity in the refracting lane, but when confronted with real world challenges, the quality of their vision may not be as good as they expected. Unhappy patients have raised the bar of ophthalmologists’ awareness. Ophthalmologists have been able to take that information and apply it to IOL technology to improve the performance of IOLs.
(Images courtesy of Arthur P. Ginsburg, MD.)
Mark Troski, MD, FRACO, FRACS: Ophthalmologists have new technology to achieve excellent refractive results. I always tell patients the Tecnis Z9000 IOL (Advanced Medical Optics, Inc. [AMO], Santa Ana, Calif.) has the “Wow!” factor. Although other IOLs may provide results approximating emmetropia, I believe the Tecnis provides a high level of visual quality. Patients are astounded with how clear their vision is and will discuss that with friends and relatives, which helps word-of-mouth marketing.
Wallace: What other factors influence your selection of IOLs?
Masket: Cosmetics is an important consideration for my patient base. I work in Los Angeles and some of my patients are on camera and are concerned about abnormal reflections from their eyes.
One of the impressive features of the Tecnis is that people look natural. People looking at patients will not see the extra Purkinje image that causes reflections on the lens that are sometimes associated with other IOLs.
Contrast sensitivity loss
Wallace: For many clinicians, contrast sensitivity measurement is not routine; it is almost considered a research arm of visual evaluation. However, measuring contrast sensitivity is becoming an important part of clinical practice. How has contrast sensitivity played a role in your practices, with clinical research, patient care in general and assessing patient visual function?
Roberto Bellucci, MD: Elimination of spherical aberration is correlated with increased contrast sensitivity. Ideally, the ocular system is neutral in terms of spherical aberration. The natural crystalline lens corrects the spherical aberration of the cornea. Spherical IOLs do not correct spherical aberration, which is why the Tecnis aspheric IOL was developed. Cataract surgery can be seen as an opportunity to correct spherical aberration.
Contrast sensitivity plays a significant role in functional vision; it is one of the reasons why patients have cataract surgery. Some of my patients who request cataract surgery have 20/20 visual acuity with or without correction, so the loss in visual acuity or the presence of refractive error is not the only motivation for surgery.
Ophthalmologists knew that older patients needed more light to see; however, the reason more light was needed was not clear. Some clinicians thought that more light was needed because the retina becomes less sensitive with age, but it is now understood that the main factor is the loss in contrast sensitivity that occurs with age. Therefore, improving contrast sensitivity is important because patients notice the loss when performing daily activities. Functional vision is based more on contrast sensitivity than on visual acuity. Patients with low degrees of visual acuity can identify objects if they retain some contrast sensitivity. In Europe, especially in Italy, a large percentage of the population is getting older, and millions of older people drive and watch television. In facing these new visual requirements of the aging population, contrast sensitivity is a significant visual ability and should be improved in patients.
Masket: In reference to vision tests, testing the quality of patients’ vision with Snellen acuity is illogical. Herman Snellen developed this chart in the 1860s and clinicians are still using it today. Visual quality should be measured in a way that is analogous to measuring hearing. When clinicians test hearing, they test both pitch and tone. For example, when considering sound, one can hear different notes at the same pitch, or the same note at different pitches, but in the real world people hear varying sounds at differing pitches. Snellen acuity does not match what is actually seen in the world. It does not match how the visual system works and is an outdated measurement system.
Today, clinicians want to assess how people see different objects, at different sizes, against different backgrounds; this is the way the visual system works. With loss of contrast sensitivity, patients may have more difficulty seeing a person than seeing a small detail varying with the lighting conditions. The concept of Snellen acuity testing should be dispelled. Contrast sensitivity function should be valued as the most accurate means to measure functional vision.
Manfred Tetz, MD: Visual acuity is an angular two-point discrimination, and contrast sensitivity is visual contrast perception. Clinicians should use a term that describes the multi-functionality that is inside the eye to explain vision.
Bellucci: Because ophthalmologists do not test it regularly, patients are usually unaware of what contrast sensitivity is.
Troski: I implanted the Tecnis IOL into a patient who is a professional photographer, who had a posterior subcapsular steroid-induced cataract. Before his procedure, his vision was 6/18. After the procedure, he said “I cannot imagine ever seeing better than I see with this IOL.”
Masket: Ophthalmologists are now learning to understand patient complaints better, regardless of their particular professions. Clinicians are alerted to loss of contrast sensitivity when patients complain of difficulty driving at night or not seeing a golf ball on the tee. These patients may not have cataracts that look significant to clinicians, but they can be significant to the patients.
Tetsuro Oshika, MD: I find that the current method for measuring contrast sensitivity lacks precision. When my colleagues and I conducted a bilateral study on 25 patients comparing the Tecnis Z9000 IOL and the CeeOn 911 IOL (AMO), we found that the score was too rough in the current contrast sensitivity measurement system. More precision can be achieved by using smaller intervals between the neighboring contrast levels.
In our bilateral study, the Vector Automated Vision System (Micro-Vu Corp., Windsor, Calif.) was used to measure contrast. Ophthalmologists must correct refractive error first because minor refractive error influences the result of small changes in contrast sensitivity.
Currently, my colleagues and I are working on developing a system that measures contrast more simply and that can also pick up more sensitive differences between the eyes.
Natural lens shape changes over time
Wallace: What is happening to the lens beyond opacification as we age?
Masket: Contrast sensitivity loss is associated with changes in lens shape throughout a person’s life. Virtually all corneas have positive spherical aberration, which is balanced in youth by the shape of the lens and its associated negative spherical aberration. Over a lifetime, with growth, the lens develops more positive spherical aberration and no longer balances with the cornea (Figure 2). It is important for clinicians to understand this principle because it explains why many elderly patients who upon examination appear to have normal visual function but actually have increased complaints. The complaints are due to loss of contrast.
Wallace: Clinicians are beginning to understand the importance of doing more for patients than just replacing a lens that has positive spherical aberration with another lens that has positive spherical aberration. The lens should be replaced with one that creates a more youthful quality of vision — not just a clear lens, but one that negates the positive asphericity of the cornea and restores the balance of the optical system.
Colvard: Adrian Glasser, PhD, and Melanie Campbell, PhD,1 demonstrated that, in the youthful eye, optical coupling between the cornea and the lens reduces spherical aberration. Ophthalmologists must try to reestablish this youthful coupling during cataract surgery.
Reestablishing the balance between the two focusing elements of the eye is critical, not only for older patients, but also for younger patients who have cataracts. In fact, ophthalmologists can argue that younger patients need aspheric IOL technology such as that offered by the Tecnis IOL more than older patients.
Tecnis improves night driving simulator performance
Wallace: Patients want IOLs that provide good quality vision for conducting daily life activities such as night driving. Which IOLs would you select for patients who complain of problems seeing when driving at night?
Colvard: The Tecnis IOL is the only IOL that has specific Food and Drug Administration-approved indications for improving night driving simulator performance. These claims are based on an FDA-monitored, randomized masked trial, which compared the Tecnis IOL to an acrylic IOL.2 Testing, using the ETDRS chart, showed that the Tecnis IOL demonstrated better best-corrected visual acuity (BCVA) than the acrylic IOL.
(Image courtesy of AMO.)
The finding of improved BCVA with the Tecnis IOL is surprising and intriguing. The finding suggests that IOLs that are not corrected for spherical aberration, even with high-contrast targets, may have an increased smudge of blur circles, which slightly diminish acuity. More study is needed in this area.
Night vision simulation, however, was the most important and dramatic arm of the study. In the testings, one eye was covered and ocular dominance was randomized. The study was double-masked, so neither the technician nor the patients knew which eye had a Tecnis IOL and which had the acrylic IOL. The simulation studied recognition and identification of targets under night driving conditions. The Tecnis IOL performed better in most areas of measurement, especially under low levels of illumination. Simulation demonstrated that in a “rural setting,” traveling at 55 miles per hour, patients implanted with the Tecnis IOL were able to identify a pedestrian 45 ft. earlier than patients implanted with the acrylic IOL (Figure 3).3 This provides for an average of about 0.5 seconds more time to perceive and react to a pedestrian hazard. In contrast, the federally mandated third brake light improves braking time by only 0.35 seconds.
(Image courtesy of AMO.)
Wallace: Discuss how IOL design impacts functional vision.
Tetz: My colleagues and I have researched how sharp an optic edge must be to prevent posterior capsule opacification (PCO).4
We used a cell experimental model to test how sharp an edge must be so that cells growing inside toward the center are hindered by the edge alone, not by the pressure, or shrinkage, of the capsule. We found that the area defining deviation from an exact rectangle must be below 12 µm2 to 15 µm2 in order to prevent lens epithelial cells from spreading across the IOL.
Haptics design and IOL centration
Wallace: How do haptic characteristics affect centration?
Colvard: David Apple, MD, and colleagues showed that a continuous 360° square edge configuration, uninterrupted by haptic insertion, creates the most effective barrier to cell migration (Figure 4 and Figure 5).5 When implanting the Tecnis IOL, surgeons insert the haptics anteriorly to avoid creating a breach that would allow cells to slide under the IOL. The problem with one-piece IOLs is that the haptic junction is broad and can act as a bridge for lens epithelial cells (LECs) to freely migrate onto the lens surface. Donald Nixon, MD, performed a study comparing LEC migration behind the optic of a three-piece and a one-piece IOL in the region of the optic-haptic junction (Figure 6).6 In the early postoperative period, neither IOL showed any LEC migration behind the IOL optic. However, over time, LECs could be visualized behind the optic at the optic-haptic junction of the one-piece IOL while the area of the optic-haptic junction was clear of LECs in the three-piece IOL.
(Image courtesy of Michael Colvard, MD, FACS.)
Tetz: An additional advantage of the Tecnis IOL is its haptic design. In my previous studies, my colleagues and I found that a C-shape and broad contact of the posterior surface of an IOL optic along the entire periphery of the capsular bag are advantageous.7 The Tecnis IOL haptic leaves the optic in a 90° angle, and a built-in elbow starts the curvature, which actually transfers the forces to the broad surface, rather than at one point, as seen in IOLs that have an oblique angle. This design may help IOL centration.
Wallace: How does centration influence the performance of the Tecnis IOL? What have been the results of centration studies after Tecnis IOL implantation?
Mester: Centration of the Tecnis wavefront-designed optic was thought to be an important topic because new products claim to be less sensitive to decentration than the Tecnis IOL. My colleagues and I measured the centration of the Tecnis IOL in two studies and found no significant decentration. Problems with decentration are unlikely when surgery is performed uneventfully, the IOL is implanted with both haptics in the capsular bag, and capsulorrhexis is performed correctly.
Previously published data revealed that the critical amount of decentration that an aspheric IOL can tolerate is 0.4 mm. New studies that involve an asymmetric eye model and polychromatic light, found that the Tecnis IOL can theoretically tolerate up to 0.8 mm of decentration and 10° of tilt.8 This is far beyond the clinically assessed decentration of IOLs published in modern cataract surgery literature9-11 and what my colleagues and I found in our studies.
(Image courtesy of Michael Colvard, MD, FACS.)
Wallace: Theoretically even with up to 1 mm of decentration, the wavefront-designed optic of the Tecnis IOL would be associated with enhanced optical outcomes compared to a spherical IOL.
Colvard: Several papers have demonstrated that, even with a variety of haptic designs, the average decentration of IOLs is 0.2 mm, and the average tilt is 2°.9-11 In my experience, the Tecnis IOL provides good centration. If the capsulorrhexis is intact and the Tecnis IOL is placed within a stable capsular bag, centration of this IOL is excellent.
Wallace: Are there other surgical factors that influence centration?
(Images courtesy of Donald R. Nixon, MD.)
Masket: An unexplained phenomenon observed with other IOLs is that any IOL that has a tendency to decenter will decenter superiorly if the haptics are oriented horizontally. Therefore, clinicians should place the haptic tension primarily from 6 o’clock to 12 o’clock so that superior decentration does not occur.
Wallace: Many surgeons prefer longer haptics so that they can place an IOL in the sulcus if necessary, although a 12-mm haptic length would probably do well in the sulcus. Have you had any experience with that?
Masket: I use the 12-mm overall IOL diameter, as there is a greater incidence of transient striae in the capsule with the 13-mm haptic.12
Wallace: What devices and techniques do you use when implanting the Tecnis IOL?
Troski: The Tecnis IOL is easy to inject using the Unfolder Silver implantation system (AMO). Later this year, the Tecnis acrylic IOL will be available for insertion with the Unfolder Emerald delivery system (AMO).
Just by rotating the injector, the trailing haptic nearly always enters the bag easily. However, if the viscoelastic is inserted into the cartridge for the inserter early, the trailing haptics may get stuck. Healon (1% sodium hyaluronate, AMO) ophthalmic viscosurgical device becomes difficult to remove if left in for a long time. As a tip, surgeons should not use Healon too long before implanting the IOL.
When teaching other surgeons how to use the Unfolder, I use a significant amount of Healon. If the insertion does not feel right and there is resistance, the surgeon should trust this feeling and stop. This is the time to recheck that the IOL has been correctly loaded.
Wallace: The Unfolder injection system seems to have the ability to let ophthalmologists know when to stop injection.
Colvard: Another advantage of the Unfolder system is that it allows the Tecnis IOL to be implanted through a 2.7-mm incision without enlargement.
Bellucci: I have had opportunities to test other injectors. With other injectors, loop damage can occur during IOL loading or injection, and in some instances, the loop completely breaks, and the IOL needs to be replaced. In addition, an IOL can show a “bite” after implantation and has to be removed. The Unfolder system does not seem to be associated with these problems.
Masket: An issue that may arise with the Unfolder system is that the leading haptic may not be fully extended, appearing as if it is looped over itself in the cartridge. Clinicians should take the time to straighten the leading haptic before implanting the IOL into the eye.
Wallace: How does the wavefront-designed Tecnis optic compare to other optics?
Masket: With the AcrySof SN60WF (Alcon Laboratories, Inc.), the aspheric surface is on the posterior of the optic. I have noted variable optical results of surgery with this IOL.
Bellucci: I implanted a series of the L161AO IOLs (Bausch & Lomb, Rochester, N.Y.) and measured the aberrations in the implanted eyes. There was no statistically significant difference between the spherical aberration at the corneal plane and the spherical aberration of the entire eye in patients who received the L161AO. The difference in induced spherical aberration as compared with the Tecnis IOL was statistically significant, but the difference as compared with aphakic eyes was not. It appears that the L161AO IOL does not correct spherical aberration already present on the cornea.
Oshika: My colleagues and I performed our bilateral study on 25 patients in Japan. In each patient, we implanted the Tecnis Z9000 IOL in one eye using forceps and the CeeOn 911 IOL in the contralateral eye. The study compared visual function and corneal spherical aberrations. The results illustrated that the Tecnis IOL was successful in reducing spherical aberrations. Eyes implanted with the CeeOn 911 IOL had positive spherical aberration.
Although no significant difference in visual acuity or contrast sensitivity was found, eyes implanted with the Tecnis IOL appeared to have better vision results than eyes implanted with the CeeOn 911 IOL.
Further, in our clinical study, we asked patients to identify which eye they preferred and found no significant difference between the two IOLs. Patients who were masked as to which IOL was implanted in each eye, selected the eye that had fewer refractive errors in lower-order aberrations.
(Images courtesy of Tetsuro Oshika, MD.)
My colleagues and I also performed a simulation study based on data drawn from the bilateral study. We input aberration data into computer software to produce a simulation of a retinal image. Retinal image was dependent on pupil size. If the simulated pupil size was 2 mm or 3 mm, then the retinal image did not differ greatly between the two eyes. If the pupil diameter was 4 mm or 5 mm, then a clear difference was visible on the retinal image. The eyes implanted with the Tecnis IOL had clearer retinal images (Figure 7). From these studies, we concluded that Tecnis IOL can improve a patient’s retinal image, dependent on the pupil size. The larger the pupil, the greater the difference will be. On the other hand, patient perception may play a role. Older patients with smaller pupils may not be able to recognize the difference between the two IOLs. Younger patients may be more able to recognize differences between the two IOLs’ effects on visual quality than older patients, especially when considering mesopic vision at night.
Wallace: Are there any patients who would not benefit from aspheric IOLs?
Mester: To get an impression of the individual performance of the Tecnis IOL, my colleagues and I investigated postoperative ocular spherical aberration in different refraction situations. Patients with emmetropia or hyperopia received the greatest benefit from the Tecnis IOL (Figure 8). Patients implanted with Tecnis IOLs with a power of 12 D showed a slight overcorrected spherical aberration. Patients with high myopia may not benefit from the Tecnis IOL. It is necessary to look at the biometry of the eyes that receive such IOLs.
Masket: Lower power IOLs may not do much to reduce corneal aberrations due to the nature of the optics. Some patients, by virtue of their corneal shape, also would not benefit from having this type of IOL, such as patients who have high degrees of a prolate cornea. In contrast, patients who have had LASIK to correct myopia and later undergo cataract surgery benefit from the concept of the Tecnis IOL, particularly if they have had a traditional, rather than custom, ablation. Tecnis IOLs are also valuable in patients with a large degree of induced positive spherical aberration.
Colvard: If a spherical IOL is implanted in a patient who has had LASIK to correct myopia, contrast problems secondary to spherical aberration may be magnified. Implanting the Tecnis IOL in patients who have had LASIK to correct myopia is sensible.
Wallace: Tecnis will soon be available with a hydrophobic acrylic optic. Will this change your IOL choice?
Bellucci: Some patients are not suitable for silicone IOL implantation, such as those with diabetes and those who undergo posterior segment surgery combined with cataract surgery. If clinicians want to remove an epiretinal membrane, they should not select a silicone IOL due to the possible posterior segment complications requiring silicone oil injection. This problem does not exist with acrylic materials.
Mester: For routine cases, I use third-generation silicone IOLs because the material is clear. I find the high refractive index silicone IOL easy to insert, particularly with the higher power IOLs. In patients who are at risk for posterior segment problems, I prefer to implant acrylic IOLs.
Tetz: Any kind of acrylic IOL would have to match the Tecnis silicone IOL’s high standard features, such as centration and "intelligent" asphericity.
Colvard: Silicone is a better material with proven optical quality and, in my opinion, is equal in biocompatibility to hydrophobic acrylic materials. With the exception of the few patients who are likely to require injection of silicone oil, I find no reason to use an acrylic IOL over a silicone IOL.
A perception still persists in ophthalmology that hydrophobic acrylic material is somehow more biocompatible than silicone material, but this perception is not supported by laboratory research. The idea that hydrophobic acrylic materials are more biocompatible than modern silicone materials is a clinical myth that was fostered by low capsular opacification rates in early acrylic square edged IOLs. Ophthalmologists now know that these low opacification rates were due to edge configuration rather than the acrylic material.
(Figure courtesy of Ulrich Mester, MD.)
Bellucci: The hydrophobic acrylic IOL could attract more surgeons to the Tecnis lens and wavefront technology concepts, especially surgeons who like acrylic or new surgeons who sometimes think acrylic is easier to handle than silicone. However, the injector systems now available for the Tecnis IOL will soon dispel the notion that acrylic is easier to handle.
Oshika: The Tecnis acrylic IOL is set for approval in Japan in October 2005. The IOL will have the same modified prolate surface as the Tecnis silicone IOL, but will be produced with Sensar hydrophobic acrylic material and have blue PMMA haptics.
Hydrophobic acrylic material is an exciting option for the Tecnis IOL and I would select it for my patients. Although the currently available Tecnis IOL is successful in reducing spherical aberrations, I look forward to future advances. It would be beneficial to have an IOL that reduces spherical aberration.
Future of IOLs and cataract surgery
Wallace: Please discuss future activity in regard to reduction of aberrations associated with new IOL designs, such as the effect on chromatic aberration.
Mester: Some evidence suggests that the next step in improving optical quality may be to correct chromatic aberration and that the combination of reducing spherical aberration and reducing chromatic aberration would be effective. Other higher order aberrations are not treatable with current IOL designs because the IOLs must be rotationally symmetric.
Wallace: How does reducing spherical aberration influence other aberrations? Is there a secondary effect to these other aberrations by improving spherical aberration?
Tetz: By considering the magnitude of the higher order aberration, the root mean square and the part of the spherical aberration within that root mean square in wavefront analysis, clinicians see that in a living system, spherical aberration accounts for most higher order aberrations.
There will also be a move toward bioptics filters (final fine-tuning correction with additional laser surgery following IOL implantation), which will give clinicians more options in completely correcting the system.
Bellucci: Currently, I offer bioptics to demanding patients when I am unsure if a multifocal implant will attain the high level of precision they request. I perform laser surgery on these patients 1 month after implant surgery. Patients who are not satisfied with the results of the first procedure undergo LASIK to reach emmetropia.
Surgeons should implant IOLs with a platform that ensures that the IOL will not be displaced later. LASIK or customized LASIK can then be performed to correct the remaining refractive error or the remaining aberrations on the cornea.
Tetz: The future could be bright if ophthalmologists were to customize any kind of reduction in aberration in an eye and have that implemented in an IOL that corrects for that specific eye only. However, spherical aberration and chromatic aberration, which is spherical aberration separated into different wavelengths, are most important for patients’ vision. Customized IOLs would often be sought if available.
Wallace: Moving toward customizing IOLs emphasizes the current shift in cataract surgery from focusing on solely giving patients good visual acuity to giving patients good quality of vision.
Although patients would benefit from customized IOLs, the latest advances in IOL designs, including the wavefront-designed aspheric Tecnis IOL, have been shown to improve overall functional vision.
I would like to thank the panel for their comments, Ocular Surgery News for organizing this symposium and Advanced Medical Optics, Inc., for providing its support.
- Glasser A, Campbell MC. Biometric, optical and physical changes in the isolated human crystalline lens with age in relation to presbyopia. Vision Res. 1999;39:1991-2015.
- Tecnis IOL package insert. Advanced Medical Optics, Inc.
- McBride DK, Matson W. Assessing the significance of optically produced reduction in braking response time: Possible impacts on automotive safety among the elderly. Arlington, Va: Potomac Institute for Policy Studies; May 2004. PIPS-50-03.
- Tetz MR, Wildeck A. Evaluating and defining the sharpness of intraocular lenses. Part I: Method for the evaluation of influence of intraocular lens optic design on the growth of lens epithelial cells in vitro. J Cataract Refract Surg. In press.
- Werner L, Mamalis N, Pandey SK, et al. Posterior capsule opacification in rabbit eyes implanted with hydrophilic acrylic intraocular lenses with enhanced square edge. J Cataract Refract Surg. 2004;30:2403-2409.
- Nixon D. Lens epithelial cell migration at the haptic-optic junction of a single-piece acrylic IOL. Poster presented at: the Annual Meeting of the American Society of Cataract and Refractive Surgery. Monday, April 18, 2005. Washington, D.C.
- Apple DJ, Solomon KD, Tetz MR, et al. Posterior capsule opacification. Surv Ophthalmol. 1992;37:73-116.
- Piers P, Weeber H, Artal P. A Verified Model for Customized IOLs. Presented at: 6th International Congress on Wavefront Sensing and Optimized Refractive Corrections. February 12, 2005; Athens, Greece.
- Akkin C, Ozler SA, Mentes J. Tilt and decentration of bag-fixated intraocular lenses: a comparative study between capsulorrhexis and envelope techniques. Doc Ophthalmol. 1994;87(3):199-209.
- Hayashi K, Harada M, Hayashi H, Nakao F, Hayashi F. Decentration and tilt of polymethyl methacrylate, silicone, and acrylic soft intraocular lenses. Ophthalmology. 1997;104(5):793-798.
- Mutlu FM, Bilge AH, Altinsoy HI, Yumusak E. The role of capsulotomy and intraocular lens type on tilt and decentration of polymethylmethacrylate and foldable acrylic lenses. Ophthalmologica. 1998;212(6):359-363.
- Vasavada AR, Trivedi RH. Posterior capsule striae. J Cataract Refract Surg. 1999;25:1527-1531.