November 2007

 

CATARACT/ IOL

 

PCO prevention with square-edged IOLs


by Rich Daly EyeWorld Contributing Editor

 

 

Effect of sharp edge acrylic IOL (left) on PCO compared to round edge acrylic IOL (right), three years after cataract surgery.

Effect of sharp edge silicone IOL (left) on PCO compared to round edge silicone IOL, one year after cataract surgery.

Effect of sharp edge PMMA IOL (left) on PCO compared to round edge PMMA IOL (right) Source: Oliver Findl, M.D.

No advantage is seen among the various post-op anti-inflammatory treatments that aim to influence PCO development The most common long-term complication after cataract surgery is best prevented by the use of square-edged IOLs, according to a review of previous research on the subject. The review reinforced previous findings that chronicled the inability of various post-op anti-inflammatory treatments to also reduce the development of posterior chamber opacification (PCO).

The review of 53 prospective, randomized, and controlled trials with a follow-up time of at least 12 months was published in the Cochrane Database of Systematic Reviews.

The review reinforced the widely reached conclusion that due to the highly significant difference between round and sharp-edge IOL optics, IOLs with sharp posterior optic edges should be preferred. Most round-edge IOLs have already disappeared from the market.

Nick Mamalis, M.D., professor of ophthalmology, Moran Eye Center, University of Utah, Salt Lake City, said the “thorough and exhaustive” review by Oliver Findl, M.D., Department of Ophthalmology, Medical University of Vienna, Austria, and co-investigators drew reasonable and unsurprising conclusions from the available literature.

Although a good treatment for PCO is available with the use of a neodymium:YAG laser capsulotomy, Dr. Mamalis said, the treatment’s costs and the small but significant risk of complications—along with the visual impairment brought by PCO—reinforce the need to delay or eliminate it. David F. Chang, M.D., clinical professor, University of California, San Francisco, pointed out that due to the frequency of cataract surgery, diagnosing and treating PCO represents a major cost for any healthcare system. Also, PCO is a huge problem in developing countries where patients with poor access to care lose the hard earned benefits gained from their cataract surgery.

The findings echoed the large amount of literature that has shown the square edge in IOLs is better at retarding lens epithelial cells and PCO than the round edge. The benefits of the square are complimented by the way that edge fits with the posterior capsule and the so-called capsular bending that previous research has identified, he said.

“It’s more than just a square edge but a square edge is an important factor,” Dr. Mamalis said, about PCO-prevention efforts.

The square edge also can overcome problems with the materials. If material used is more conducive to PCO it is very important that there be a 360-degree square edge to try to counteract the PCO, according to Dr. Mamalis’ research.

The review found no clear difference in the ability of different optic materials to prevent PCO, except for hydrogel IOLs, which showed more PCO than the other materials.

“Randomized studies also have shown that as long as the optic edge is truncated, both hydrophobic materials, silicone and hydrophobic acrylic, perform equally well,” Dr. Chang said.

“Hydrogel materials, perhaps because of their higher water content, seem to be too biocompatible with respect to lens epithelial cell replication and migration,” Dr. Chang noted. Further research is needed to conclusively demonstrate whether there is a PCO-prevention difference between the widely used hydrophobic acrylic and silicone IOLs.

Although he said he agreed with the review’s finding regarding hydrophilic IOLs, Dr. Mamalis said the review did not support the theory of some that hydrophobic IOLs would allow less PCO than other materials.

“There was some idea that the hydrophobic materials are stickier and that the material has a tendency to retard PCO but that has not been consistently shown in the literature, so I don’t disagree with their result,” he said.

The review also found that the small but growing number of evidence-based research indicates that the choice of post-op anti-inflammatory treatment does not seem to influence PCO development. The review found little benefit in the recent effort to provide medications during or after surgery to deplete or inhibit regeneration of remaining lens epithelial cells, except for a discontinued treatment with an immunotoxin (MDX-A). The review did conclude that more research is needed to show this conclusively.

“They found what we all found in that we’re disappointed in that [anti-inflammatory medicines] have not been shown to significantly affect the rate of PCO,” Dr. Mamalis said.

The results make it clear, Dr. Chang said, that IOL design and surgical factors, such as an overlapping capsulorhexis, hydrodissection, and thorough cortical clean-up are much more important than post-op pharmacology.

Next steps needed

The review authors noted that more PCO research is needed to provide prospective randomized trial data on the effect of posterior capsule polishing, capsular tension rings, and of primary posterior capsulorhexis on PCO. Also needed is the use of a standardized method for quantification of PCO.

“A ‘common’ PCO scoring method would make the comparison of different trials easier,” the authors noted.

Also yet unsettled, Dr. Chang noted, is the key issue of whether PCO rates over the long term will be higher with the single-piece AcrySof acrylic IOLs (Alcon, Fort Worth, Texas), which do not have a 360-degree posterior sharp edge. The review authors advocated a five-year follow-up period to answer this question, which none of the published studies yet provide.

Editors’ note: Dr. Mamalis is a contract researcher for Advanced Medical Optics (AMO, Santa Ana, Calif.), Alcon (Fort Worth, Texas), Bausch & Lomb (Rochester, N.Y.), and Rayner (East Sussex, U.K). Dr. Chang is a consultant for AMO, Alcon, and Visiogen (Irvine, Calif.).

Contact Information

Chang: 650-948-9123, dceye@earthlink.net

Mamalis: 801-581-6586, nick.mamalis@hsc.utah.edu

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