Studies point to aspects of best IOL designs
Pathology studies help surgeons focus on designs that cut down on PCO, ACO and capsular shrinkage.
With the large number of IOLs on the market, it can be difficult for surgeons to figure out which is best for what circumstance. Marketing is of little help, because each new lens is touted as better than all those before. What may help in this decision-making process are studies that have looked at lenses in the eye over many years. Though often not hyped like clinical studies of new IOLs, pathology studies can help surgeons learn from the experience of past surgeries.
Much of this type of research is done at the Center for Research on Ocular Therapeutics and Biodevices at the Medical University of South Carolina’s Storm Eye Institute. There David J. Apple, MD, and his team of researchers have examined some 9,000 explanted IOLs from eyes obtained postmortem over the course of 17 years.
Recent studies by this group have identified lens styles that may help surgeons cut down the incidence of posterior capsular opacification (PCO) and anterior capsular opacification (ACO) and capsular shrinkage in their patients. They have also identified late complications in some IOL styles that may serve as a warning of future problems in eyes that seem quiet now.
This article reviews some of their recent work, as well as related work by another author. We hope it offers some guidance in surgeons’ selection of IOLs for their patients.
PCO on the way out
FIGURES COURTESY DAVID J. APPLE, MD, LILIANA WERNER, MD, PHD, AND SURESH K. PANDEY, MD. |
Dr. Apple and his team have proposed that PCO may be eradicated in the near future if surgeons adopt some modifications to their current techniques and choose their IOLs carefully.
Dr. Apple said the overall incidence of PCO and hence the incidence of Nd:YAG laser posterior capsulotomy is now rapidly decreasing from rates as high as 50% in the 1980s and early 1990s. He said the surgical tools and IOLs are now available to bring the PCO rate down to single digits.
“Careful application and use of these tools by surgeons can genuinely lead in the direction of virtual eradication of secondary cataract, the second most common cause of visual loss worldwide,” Dr. Apple said.
Dr. Apple and colleagues, in a well-known study published in Ophthalmology last year, identified six factors regarding surgical technique and IOL choice that have drastically reduced the incidence of PCO.
The researchers based their findings on 5,416 globes with posterior chamber IOLs obtained postmortem received from Lions Eye Banks between 1988 and 2000.
Nd:YAG rates were used as the main tool to determine the incidence of PCO in all eyes and identify which IOLs seemed to work best at limiting PCO rates. Lenses not implanted in the United States or not yet approved for domestic implantation were not included in the study.
The results showed that Nd:YAG rates were in the 20.3% to 33.4% range with older designs but fell to 0.9% to 17.1% in newer foldable designs. In comparing foldable to rigid designs overall, the foldable designs were much lower at 14.1% than the rigid at 31.3%.
Dr. Apple’s team of investigators analyzed eight IOL styles commonly implanted in the United States, including single- and three-piece designs with rigid PMMA optics and six foldable IOL designs.
The foldable silicone IOLs included single-piece plate-haptic lenses, both the large-hole and small-hole designs, and three-piece silicone opticpolyimide haptic lenses. Also included was the hydrophobic three-piece acrylic optic-PMMA haptic IOL, a three-piece silicone optic-polypropylene haptic IOL and a three-piece silicone optic-PMMA haptic IOL.
The study did not investigate any non-U.S.-made lenses, the CeeOn Edge 911 IOL, or any hydrogel or hydrophilic acrylic designs, including the Hydroview lens and the MemoryLens.
The investigators used a Miyake-style posterior photographic technique to identify the presence or absence of Nd:YAG laser posterior capsulotomy.
Of all the IOLs tested, Dr. Apple and colleagues were most impressed by the Alcon AcrySof three-piece IOL, which stabilized at the previously unheard of Nd:YAG rate of less than 1%.
To further decrease the rate of PCO, the authors suggested surgeons should strive to minimize the number of lens epithelial cells and amount of cortex remaining in the capsular bag after cortical cleanup. However, if unwanted proliferative cells do remain, the researchers suggested creating a secondary line of defense by erecting a barrier to block growth of cells from the equatorial region toward the visual axis.
The six factors
Dr. Apple and his team identified six factors they believe can help in preventing or at least delaying PCO. Three are IOL-related and three are technique-related.
Hydrodissection. The authors noted that most surgeons have had a fatalistic attitude regarding removal of lens cortex and cells during phacoemulsification, because it is commonly assumed that removing all or even most equatorial cells from the bag is impossible.
Dr. Apple and colleagues explained that with careful, copious hydrodissection, the operation is easier and faster, cortex and cell removal is more thorough and formation of Soemmering’s ring is minimized. The entire lens cortex and nucleus can be extracted, often without the need for cortical aspiration, if cortical cleaving hydrodissection is employed. The authors say the necessary tenting up of the anterior capsule is best achieved using a cannula with a bend at the tip, allowing an upward flow of fluid to efficiently separate capsule from cortex.
In-the-bag IOL placement. The authors suggested that in-the-bag IOL placement is extremely important in reducing the incidence of PCO. In-the-bag fixation functions primarily to enhance the IOL-optic barrier effect. The barrier effect is functional and maximal when the lens optic is fully in the bag, in direct contact with the posterior capsule. When one or both haptics are out of the bag, a potential space exists that allows an avenue for ingrowth of cells toward the visual axis.
CCC smaller than the IOL optic diameter. Creating a continuous curvilinear capsulorrhexis (CCC) with a diameter slightly smaller than that of the IOL optic places the CCC edge on the anterior surface of the optic and helps keep the optic in the capsular bag. Placing the CCC edge over the optic helps provide a tight fit, or “shrink wrap,” of the capsule around the optic and also helps sequester the compartment inside the capsule containing the IOL optic from the surrounding aqueous humor. This may help protect the contents of the capsule from at least some potentially deleterious factors within the aqueous, the authors say, especially some macromolecules and some inflammatory mediators.
Biocompatibility. The biocompatibility of the lens material must be good. The authors said the Alcon AcrySof IOL scored well with this criterion, both with respect to Soemmering’s ring formation and PCO and also with respect to ACO. However, they stated that further study is necessary to assess the overall role of biocompatibility in the pathogenesis of PCO.
Tight fit. The authors suggest that posterior angulation of the IOL haptic and posterior convexity of the optic also assist in reducing PCO. Anything that will create a tight fit of the posterior capsule against the back of the IOL optic should be efficacious, they said. The relative “stickiness” of the IOL optic biomaterial may help create adhesion of the capsule and IOL optic.
Barrier effect. The barrier effect of the lens edge seems to be a major factor in reduced PCO, the authors said. A truncated, square-edged optic seems to be effective in causing a blockade of cells at the optic edge, leaving the posterior capsule free of cells. The enhanced barrier effect provided by this optic geometry probably functions as an “icing on the cake” by providing an additional reserve factor, in addition to the five above, that is of importance in helping reduce the overall incidence of visually significant PCO.
The authors noted that a possible disadvantage of the truncated edge is the potential formation of visual aberrations including glare, halos or crescents. They said, however, that subtle changes in manufacturing are now helping to alleviate these complications.
Capsular shrinkage differences
While PCO is a well-known complication of cataract, anterior capsular opacification (ACO) and capsular shrinkage are also significant complications that have been detailed in recent studies.
From the same research center, a study published in 2001 by Liliana Werner, MD, PhD, and colleagues confirmed their previous histopathologic observations that the rate of ACO is lower with acrylic lenses and higher with plate-haptic silicone IOLs.
In addition, capsular shrinkage was found to be important with three-piece silicone optic-polypropylene haptic designs. Dr. Werner and colleagues concluded that IOL material and design are significant factors in the development of ACO, but they ultimately also influence the clinical presentation of capsular shrinkage.
The study was designed to evaluate the degree of ACO in human eyes obtained postmortem containing various rigid and foldable posterior chamber IOL designs and to compare the findings with clinical sequelae of capsular shrinkage.
The authors pointed out that if the anterior surface of the optic material is in contact with the adjacent posterior aspect of the anterior capsule, the remaining anterior lens epithelial cells may undergo fibrous metaplasia with capsular opacification. The report quoted previous studies that have demonstrated that the area of the anterior capsular opening seems to decrease gradually for up to 6 months postop. In addition, an excessive anterior capsular fibrosis and opacification may lead to major clinical problems and sequelae such as difficulty in examining the retinal periphery, fibrous contraction of the capsule, capsulorrhexis phimosis and IOL decentration.
The results of the study were attained from a comparative autopsy tissue study with clinicopathologic correlations. Three hundred human eyes were analyzed, with IOL implants including single-piece PMMA IOLs, single-piece silicone plate-haptic IOLs with large or small fixation holes, three-piece PMMA optic-polypropylene haptic IOLs, three-piece acrylic optic-PMMA haptic IOLs, three-piece silicone optic IOLs with PMMA or polyamide haptics, and three-piece silicone optic-polypropylene haptic IOLs.
The eyes were sectioned in the equatorial plane for gross examination of the capsular bag from a posterior view, Dr. Werner and colleagues said. The cornea and iris were then excised for evaluation from an anterior view. Three hundred eyes consecutively accessioned from January 1996 to January 2000 were selected. The investigators focused on eight lens styles commonly implanted in the United States.
The study was based on analysis of ACO in pseudophakic human cadaver eyes under an operating microscope from an anterior or surgeon’s view. ACO was scored in each eye from 0 to 4, according to the degree and area of capsule opacification. See the accompanying table (above) for a description of the grading system.
The study found that the overall differences among the IOL groups regarding the three parameters were significant. Mean ACO scores were highest with the large- and small-hole single-piece silicone plate-haptic IOLs and lowest with the three-piece acrylic optic-PMMA haptic lenses. Of 10 cases of capsulorrhexis phimosis observed in the study, seven cases were associated with three-piece silicone optic-polypropylene haptic IOLs, which also presented the highest level of mean decentration.
The process of opacification of the anterior capsule was seen to progress in stages, from fibrosis of the capsule margin to asymmetric shrinkage and displacement of the CCC opening. See the table (right) for details of the stages of progression.
Dr. Werner and colleagues determined that the hydrophobic acrylic lens presented the lowest mean decentration and ACO scores. This lens also had the lowest ACO mean score in a previous histopathologic study, the authors said.
Dr. Werner said the study findings may be of clinical significance in that, when using this IOL type, anterior capsule polishing should not be necessary in most cases, the incidence of decentration and capsulorrhexis phimosis should be minimized and a better view of the peripheral retina might be seen through a clear anterior capsule during indirect ophthalmoscopy.
She said severe ACO can be a significant clinical problem for retinal surgeons because of the difficulty of examining the retinal periphery. She also noted that the silicone plate-haptic IOL with large fixation holes has some design features that are helpful in preventing IOL decentration associated with capsular shrinkage.
ACO differences
In an earlier study, Dr. Werner and colleagues concluded that IOL design and IOL material are significant factors in the development of ACO. Their results confirmed previous clinical observations that the rate of ACO is relatively high with plate-haptic silicone IOLs. The lowest rate was found with three-piece acrylic optic-PMMA haptic IOLs.
In this study, 460 eyes obtained postmortem were examined, with implanted IOLs including single-piece PMMA, single-piece silicone plate-haptic IOLs with both large and small holes, three-piece PMMA optic IOLs with either PMMA or polypropylene haptics, three-piece acrylic optic-PMMA haptic IOLs, three-piece silicone optic-PMMA haptic IOLs, three-piece silicone optic-polyamide haptic IOLs and three-piece silicone optic-polypropylene haptic IOLs.
Dr. Werner and colleagues found that mean ACO scores were highest with the large and small hole single-piece silicone-plate lenses, while the lowest mean score was observed in the group of three-piece acrylic optic-PMMA haptic lenses.
Dr. Werner said that determining which IOL materials and designs interact less with the anterior capsule is one approach to preventing ACO, but probably not the most important. She said that while differences in ACO among lens styles are clinically noticeable, the presence of ACO generally does not lead to poor surgical outcomes. Therefore, she said, the amount of ACO is not a sufficient reason to reject a given lens style.
Rather, Dr. Werner suggested that when very dense ACO was found in her study, it was partially influenced by surgical technique. She said the major consequences of dense ACO include IOL decentration as a result of unwanted fibrous contraction of the capsule, capsular phimosis and difficulty in examining the retinal periphery.
Problems in hydrophilic acrylics
While certain styles of foldable acrylic IOL have become among the most popular in current use, the lenses as a class are not without problems. Some surgeons have expressed concerns about the long-term safety and efficacy especially of hydrophilic acrylic IOLs.
Recently in Ocular Surgery News U.S. Edition, Dr. Apple and his colleagues Dr. Werner and Suresh K. Pandey, MD, described late complications in several IOL designs (See related article from November 15, 2001). The complications included hydroxyapatite calcification in some hydrophilic acrylic IOLs and complete opacification of the IOL optic and haptic in single-piece hydrophilic acrylic IOLs from multiple manufacturers. (See photos at top of this article.) They also reported breakdown of PMMA optic material in IOLs implanted 10 years ago and more.
“The complications that are now surfacing are in general different from most that occurred during the early years of IOLs,” the doctors said. “In the 1970s and 1980s, most complications were based on faulty IOL designs and manufacture. Those described here are opacifications that usually became evident clinically 1 or more years post-operatively.
“We would have hoped that potentially severe IOL-induced problems such as these we are now seeing would have been eradicated at least by the beginning of the 1990s,” they continued. “The continuous occurrences of such complications makes it clear that modern IOLs are not perfect.”
One of the hydrophilic acrylic IOLs named by Drs. Apple, Werner and Pandey in that article was from Medical Developmental Research. The lens was distributed only outside the United States. Similar complications with the same lens are described in a recent article by Andreas Frohn, MD.
Dr. Frohn published a study of patients implanted with the MDR acrylic lens who developed unusual opacities later. Forty-one lenses were explanted. Spectroscopic findings indicated premature aging of the ultraviolet (UV)-blocking agent. The source of the opacification, Dr. Frohn said, was a change in the IOL material itself. Other tests ruled out the possibility of acids or proteins causing problems within the IOLs.
Dr. Frohn said he routinely implanted the hydrophilic acrylic IOLs, lens type SC60B-OUV, from MDR. The IOLs are manufactured from a copolymer consisting of hydrophobic PMMA and hydrophilic poly-HEMA with a water content of 26%. A UV-blocking agent is included in the material.
In the beginning, Dr. Frohn said, highly acceptable results were obtained after implantation in single cases.
In spring 1999, Dr. Frohn noted the first lens that developed a gray-whitish opacification of the central part of the IOL. The lens had to be explanted because of loss of visual acuity and glare. Meanwhile, further opacifications occurred, also in other surgical centers using this IOL in Germany.
Dr. Frohn eventually studied 41 IOLs explanted from 39 patients. The mean time between cataract surgery and IOL explantation was 423 days, with a range of 55 to 683 days. All explantations were performed because of patient dissatisfaction and not because of the visual acuity results assessed during the clinical exam.
Dr. Frohn found that typically, a central gray-whitish, sometimes yellowish opacification of the IOL occurred. The opacification affected only the inner part of the lens; a clear shell of constant thickness remained around the optical zone, as well as the haptics.
To identify the molecular origin of the opacifications, six opacified lenses and one brand new, clear MDR SC60B-OUV lens were investigated with a spectrometer. The clear, unused IOL had a smooth absorption curve, but all of the explanted, opacified IOLs showed different UV spectra. All explanted IOLs had sharp absorption peaks within the UV spectrum.
Dr. Frohn said he believes the opacification is part of an aging process of the UV protection included in the lens. The aging starts in the center of the lenses and grows to the borders. Two lenses had complete opacifications of the lens material. He noted that this was not observed in all cases because patients do not want to wait, they demand IOL explantation before the complete lens is opacified. He expects that the complete lens would be opacified in all cases over time.
For Your Information:
- David J. Apple, MD, can be reached at the Storm Eye Institute, MUSC, 167 Ashley Ave., P.O. Box 250676, Charleston, SC 29425-2236 U.S.A.; +(1) 843-792-2760; fax: +(1) 843-792-7920; e-mail:appledj@musc.edu. Dr. Apple has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Liliana Werner, MD, PhD, can be reached at the Storm Eye Institute, MUSC, 167 Ashley Ave., P.O. Box 250676, Charleston, SC 29425-2236 U.S.A.; +(1) 843-792-0777; fax: +(1) 843-792-7920; e-mail: wernerl@musc.edu. Dr. Werner has no direct financial interest in the products mentioned in this article, nor is she a paid consultant for any companies mentioned.
- Andreas Frohn, MD, can be reached at University Eye Hospital Tuebingen, Sandstr 47, D-57072 Siegen, Germany; e-mail: andreas.frohn@t-online.de. Ocular Surgery News could not confirm whether or not Dr. Frohn has a direct financial interest in any of the products mentioned or if he is a paid consultant for any company mentioned.
References:
- Medical Developmental Research Inc. can be reached at 2451 Enterprise Rd., Clearwater, FL 33763 U.S.A.; +(1) 727-793-0170; fax: +(1) 727-799-2212; e-mail: info@mdriol.com.
- Apple DJ, Peng Q, et al. Eradication of posterior capsule opacification: documentation of a marked decrease in Nd:YAG laser posterior capsulotomy rates noted in an analysis of 5416 pseudophakic human eyes obtained postmortem. Ophthalmology. 2001;108:505-518.
- Werner L, Pandey SK, et al. Anterior capsule opacification: correlation of pathologic findings with clinical sequelae. Ophthalmology. 2001;108:1675-1681.
- Werner L, Pandey SK, et al. Anterior capsule opacification: a histopathological study comparing different IOL styles. Ophthalmology. 2000;107:463-471.
- Frohn A, Dick HB. Late opacification of the foldable hydrophilic acrylic lens SC60B-OUV. Ophthalmology. 2001;108:1999-2004.