Posterior capsule opacification has been a commonly reported complication of cataract operations since the advent of extracapsular cataract surgery. And while it remains the leading cause of vision loss after cataract surgery, its incidence is declining.
In the 1980s and early 1990s, PCO occurred in 25 to 50 percent of postcataract surgery patients; today, that figure has declined to 10 percent or perhaps even lower, noted David J. Apple, MD. “Particularly if the procedure is done with good surgical technique, especially cortical [cleanup], as well as using a good lens, it is less than 5 percent,” said Dr. Apple, professor of ophthalmology and director of the David J. Apple, MD, Laboratories for Ophthalmic Devices Research at the University of Utah, Salt Lake City.
European surgeons also have noted a decline in PCO, said Gerd U. Auffarth, MD, vice-chairman in the department of ophthalmology at the University of Heidelberg in Heidelberg, Germany. “Patients who were operated on in the early 1990s had a lot of PCO if you looked at them five years later. But with the use of foldable lenses with sharp optic edges, appropriate cortical cleanup, better surgical instruments and other improvements, there continues to be a marked reduction in the incidence of PCO,” he said.
Six Critical Factors
Dr. Apple has identified six factors that are key to preventing or retarding PCO.
Three surgical factors:
- Hydrodissection-enhanced cortical cleanup
- A continuous curvilinear capsulorhexis diameter slightly smaller than that of the IOL optic
- “In-the-bag” fixation of the posterior chamber IOL
Three IOL-related factors:
- The geometry of IOLs: a square, truncated edge
- The biocompatibility of IOL biomaterials (to curtail stimulation of cellular proliferation)
- Maximal IOL optic-posterior capsule contact
Dr. Apple singled out hydrodissection-enhanced cortical cleanup as the most important of these factors. “In my opinion, that’s 85 percent of it,” noted Dr. Apple. “If you clean out the cells really well, there won’t be any of them left in the capsular bag that can lead to a secondary cataract. You can even have a fairly mediocre lens and still not have PCO if you succeed with good cortical cleanup.”
Some investigators have evaluated the intraocular infusion of pharmacologic agents (such as preservative-free lidocaine 1 percent) to improve cortical cleanup, although long-term studies of such agents have not been performed. One new development involves the PerfectCapsule device (see PerfectCapsule below).
The Role of Lens Design
“Without any doubt, the most important improvement to IOLs with regard to PCO prevention is the incorporation of the square edge,” said Liliana Werner, MD, PhD, assistant professor of ophthalmology at the University of Utah.
Since the availability of the first square-edged IOL in 1995, virtually all lens manufacturers have now introduced or are developing square- or sharp-edged IOLs. “The square edge acts as a barrier, preventing the migration of lens epithelial cells from the equatorial region onto the posterior capsule,” Dr. Werner added.
However, in cases where cortex/lens epithelial cell removal is incomplete, a possible shortcoming of the square-edge, single-piece foldable lenses is that their edges don’t continue for the entire 360-degree circumference of the optic, with a small “defect” at the optic-haptic junction, said Dr. Apple. He referred to this incomplete square edge as a possible Achilles’ heel—specifically, as a pathway where lens epithelial cells are not blocked and can migrate onto the IOL’s posterior surface.
As a result, some European and American companies are developing so-called “enhanced-edge,” one-piece lenses that extend the square edges for the full 360 degrees of the lens.
At the 2004 American Society of Cataract and Refractive Surgery meeting, Dr. Werner presented a study of a single-piece hydrophilic acrylic lens with an enhanced square optic edge.1 Her research showed that a square-edge profile present for 360 degrees around the IOL optic may help provide a totally effective barrier against cell migration.
At the 2004 Congress of the European Society of Cataract and Refractive Surgeons, Donald R. Nixon, MD, chief of the ophthalmology department at Royal Victoria Hospital in Barrie, Ontario, Canada, said that the optimal IOL would possess a 360-degree posterior square edge, a low-profile haptic-optic junction, and a tailored overall size to match the capsular bag. This lens, which he described as a “platform lens,” could then have surface modifications built in with the confidence that decentration, capsular phimosis and PCO rates would be minimal.
Design and Dysphotopsia
“Virtually every available IOL design has its specific set of unwanted visual effects, but some designs are better than others in reducing dysphotopsia,” said Steven H. Dewey, MD, who practices in Colorado Springs, Colo.
In particular, square-edged IOLs—despite their advantage in preventing PCO—continue to be associated with dysphotopsia. Dr. Dewey favors a hydrophobic acrylic IOL with a lower index of refraction and a modified edge to both preserve the posterior square edge and reduce the likelihood of dysphotopsia.
Do Biomaterials Matter?
In choosing lens biomaterials, Dr. Apple pointed out that the goal is to select a lens associated with minimal inflammation and lens epithelial cell migration. Until recently, surgeons have focused on silicone and hydrophobic acrylic IOL materials, with some research also directed at hydrophilic acrylic IOLs.
“Both second-generation silicone and hydrophobic acrylic IOLs cause the capsule to contract rather quickly, which allows rapid formation of a ‘capsular bend,’ which some researchers have associated with a decline in PCO rates,” said Dr. Dewey. “The anterior lens epithelial cells appear to respond to these materials in forming a firm fibrotic seal at the edge of the optic. The entire process is enhanced by the square posterior edge. When you’re comparing two well-designed, three-piece IOLs with square posterior edges of either second-generation silicone or hydrophobic acrylic, you’re not going to see much difference in PCO rates.”
Dr. Werner added, “In terms of PCO prevention, the IOL design does the majority of the job.”
1 Werner, L. et al. J Cataract Refract Surg 2004, in press.
Drs. Auffarth and Werner have no related financial interests. Dr. Apple has received funding from numerous companies, including Alcon, Allergan, Bausch & Lomb, Pharmacia and Rayner. Dr. Dewey is a consultant for AMO. Dr. Nixon is a paid consultant for AMO, Alcon, Allergan and B&L.
PerfectCapsule: Potential Solution
There’s a new concept in irrigation following cataract surgery: Sealed capsule irrigation. “If proven useful for the prevention of capsular bag opacification, this may eventually be incorporated as a step of the cataract/ refractive lens exchange surgical procedures,” said Dr. Werner.
And the new concept has brought a new device: PerfectCapsule. This small, flexible, biomedical-grade soft silicone device1 is placed on the anterior capsular bag after removal of the lens and before IOL implantation. Once the capsulorhexis is temporarily sealed, the surgeon can perform selective and specific irrigation of the internal capsular bag to destroy and aspirate remnants of lens epithelial cells, without exposing surrounding intraocular structures to potentially toxic substances.
PerfectCapsule is being studied in a multicenter, randomized European trial. At the 2004 Academy meeting in New Orleans, Dr. Auffarth presented data on 14 patients, in whom one eye was irrigated with sterile deionized water before a hydrophilic acrylic IOL implantation, while the other eye received implantation of the same lens without capsular irrigation.
After one year of follow-up, said Dr. Auffarth, there was a marked reduction in anterior capsular opacification, although longer follow-ups will be needed to evaluate whether statistically significant reductions in posterior opacification occur. “But the initial results are quite promising,” he added.
1 Maloof, A. J. et al. J Cataract Refract Surg 2003;29(8):1566–1568.