Baltimore—Extensive research has already led to the identification of a number of surgery- and IOL-related factors that can be targeted to reduce the occurrence of posterior capsule opacification (PCO). Investigators are continuing to evaluate new strategies to reduce its risk further in the future, said Albert S. Jun, MD, PhD, at Current Concepts in Ophthalmology, Baltimore.
"Although the rate of PCO has decreased dramatically compared with what it was in the past, it remains a significant complication of modern cataract surgery and is the most common cause of vision loss," said Dr. Jun, assistant professor of ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore. "While cataract extraction with IOL placement represents the largest expenditure for eye-related Medicare dollars, Nd:YAG capsulotomy for PCO ranks second."
Creation of a medium-size capsulorhexis, smaller than the IOL optic to allow complete overlap between the optic and anterior capsule surface, is a key element of surgical technique because it might inhibit lens epithelial cell (LEC) migration from the anterior to the posterior capsule.
Optic edge most important
Recent studies suggest lens material-related issues, including biocompatibility and IOL-capsule "adhesiveness," are less important than optic-edge geometry in preventing PCO. For example, a study published by Okihiro Nishi et al. in 2004 found no difference in PCO development when comparing acrylic and silicone IOLs, both having a square posterior edge. Similarly, in a randomized, fellow-eye controlled study including 106 eyes of 53 patients, Oliver Findl et al. found no difference in PCO when comparing eyes with a square-edge hydrophobic acrylic IOL implanted and those receiving a square-edge silicone implant.
"A sharp, truncated optic edge creates a sharp bend in the posterior capsule and therefore a barrier to block the migration of LECs toward the central visual axis," Dr. Jun explained.
The benefits of square-edge IOL geometry have been shown in other recent studies comparing round-edge and square-edge acrylic implants. Ken Hayashi et al. randomly assigned 75 patients undergoing bilateral cataract surgery to receive in one eye a foldable acrylic IOL with a sharp posterior edge (Sensar OptiEdge AR40e, AMO) and a round-edge foldable acrylic IOL in the fellow eye (Sensar AR40, AMO). The two implants are otherwise identical with respect to optic and haptic materials. After 24 months, the square-edge implant was associated with significantly less PCO as measured by Scheimpflug videophotography as well as significantly fewer Nd:YAG capsulotomies and significantly better contrast sensitivity. There was no difference between groups in mean visual acuity during follow-up.
Wolf Buehl, MD, et al. compared the same two implants in 53 patients who underwent bilateral surgery. That study featured a longer follow-up of 3 years and found the square-edge design had a benefit for reducing PCO and the need for Nd:YAG capsulotomy, and was also associated with better visual acuity.
New technology is also being developed to minimize PCO development, including capsule rings that may provide a mechanical barrier to prevent central LEC migration. In a recently published article, Burkhard Dick, MD, reported that PCO development was absent to minimal after 6 months in a series of 104 eyes that had a closed, foldable capsular ring placed into the bag prior to IOL insertion. The device used in that study had a 9.2-mm overall diameter and a square-edge design.
In an earlier study performed in rabbit eyes, Suresh K. Pandey, MD, et al. evaluated a slightly larger, 9.7-mm Hydrogel open-loop ring with a square edge. Compared with control eyes that underwent phacoemulsification only, recipients of the capsule ring had decreased central PCO. A third group of animals received a capsule ring designed to provide sustained release of 5-fluorouracil (0.25 mg/hour). However, the antimetabolite agent provided no additional benefit for reducing PCO.