November 2009

 

CATARACT/ IOL

 

Staving off PCO by design


by Maxine Lipner Senior EyeWorld Contributing Editor

   

Studying the implications lens features can have for PCO formation

Cellular PCO

Fibrotic PCO with wrinkles on the posterior capsule

Fibrotic PCO with grayish fibrotic deposits on the posterior capsule. Source: Mostafa A. Elgohary, M.D.

Spherical lenses typically have more PCO than their aspheric counterparts and will require more YAG capsulotomies, according to Joseph M. Biber, M.D., fellow at the Cincinnati Eye Institute, Cincinnati. In the July 2009 issue of the Journal of Cataract and Refractive Surgery, Dr. Biber and fellow investigators reported on the role that lens configuration can play between spherical and aspheric IOLs.

“Our primary aim was to find out if multifocal lenses had a higher PCO rate than monofocal lenses,” Dr. Biber said. In 2005, investigators began by comparing PCO and YAG rates for three lenses commonly used in their practice at the Storm Eye Institute, Charleston, S.C. These included two spherical lenses, the multifocal ReSTOR (Alcon, Fort Worth, Texas), the monofocal AcrySof Natural lens (Alcon), and an aspheric one, the monofocal AcrySof IQ lens (Alcon). They later decided to include a fourth lens, the aspheric, multifocal ReSTOR (Alcon) in the study as well. These latest results were reported at the 2009 ASCRS Symposium & Congress in San Francisco.

Investigators conducted a retrospective chart review of the lenses. Among the inclusion criteria were uncomplicated surgery, more than three months of follow up, and best corrected visual acuity of more than 20/200. Investigators found that the PCO rate for the monofocal, spherical AcrySof Natural was at 34.8%, and its counterpart, the multifocal, spherical ReSTOR, at 34.1%. Likewise, rates for the monofocal, aspheric AcrySof IQ were at 18.6% and the multifocal aspheric ReSTOR at 10%. “We found that there was no difference in PCO rate between a monofocal spherical and a multifocal spherical lens,” Dr. Biber said. “The same could be said when comparing the aspheric lenses, monofocal versus multifocal.”

Better barrier effect

Dr. Biber theorizes that the reason the aspheric lenses, which both have a symmetric biconvex configuration, fared better than the spherical IOLs with an anterior asymmetric configuration harks back to a principle put forth by David Apple, M.D. “Dr. Apple found that if you could maximize contact between the posterior surface of the optic and the posterior capsule, that would eliminate a potential space there,” Dr. Biber said. “By doing that you would prevent lens epithelial cells from migrating into that potential space and then proliferating and forming PCO.” The symmetric bioconvex configuration appears to better accomplish this. “If you were to superimpose a capsule, there is better contact in theory between the posterior lens surface and the posterior capsule if you have a symmetric bioconvex configuration,” Dr. Biber said. “Therefore, there’s less potential for space and less PCO formation—and our study found that.”

Making the YAG connection

This study also considered whether the PCO formation was visually significant. Investigators theorized that certain types of lenses might fare better in the face of PCO. “Aspheric lenses have demonstrated in other studies to have better contrast sensitivity, and monofocal lenses typically have better contrast sensitivity than multifocal IOLs,” Dr. Biber said. “PCO has been found to reduce contrast sensitivity across the board in all lens types.”

With this in mind, investigators wanted to see if there was a difference between a spherical and an aspheric lens in terms of the visual significance of the PCO. As a marker for this they used YAG capsulotomy rates. YAG rates for the spherical, monofocal AcrySof Natural were found to be 21.7% compared with a rate of 22.7% for the spherical multifocal ReSTOR. Meanwhile, YAG rates for the aspheric, monofocal AcrySof IQ lens were at 4.7% compared with 6.7% for the aspheric multifocal ReSTOR. “We found that an aspheric multifocal lens had less YAG capsulotomy than a spheric multifocal lens,” Dr. Biber said. “The same could be said when comparing the aspheric monofocal lens to the spheric monofocal lens.”

Investigators also considered whether multifocality might play a role here. This, however, did not appear to have an impact. “It was surprising to us that when we looked at a multifocal IOL it had a similar PCO and YAG rate compared to a monofocal lens in a similar category,” Dr. Biber said. “The spherical ReSTOR had a similar PCO and YAG rate compared to the AcrySof Natural lens, and the same could be said for the aspheric ReSTOR compared to the AcrySof IQ lens.”

Dr. Biber sees the take-home message here as clear cut. “Aspheric lenses should require less YAG capsulotomy compared to spherical lenses, and spherical lenses typically will have more PCO than aspheric lenses,” he said. “Also, multifocality didn’t always translate into more PCO or more YAG capsulotomies in our study.”

New lenses will soon be entering the mix. “Alcon has just made available the aspheric toric lens,” Dr. Biber said. “It would be interesting to see if there are similar findings for the newer aspheric toric lens ...”

Dr. Biber acknowledged that there were some limitations to the retrospective study that was conducted at just one institution. “With some of the new anterior imaging systems and software, it may be nice to see if there’s better posterior capsule to IOL posterior surface contact with these newer lenses in the different configurations,” he said. “That’s something that we would like to look into.”

Editors’ note: Dr. Biber has no financial interests related to his comments. Two other investigators, Helga Sandoval, M.D., and Kerry Solomon, M.D., have financial relationships with Alcon (Fort Worth, Texas) and Allergan (Irvine, Calif.).

Contact information

Biber: 843-810-9500, Jibber@cincinnatieye.com

Staving off PCO by design Staving off PCO by design
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