Eyeworld

EW CATARACT/IOL 46 February 2011 by David Spalton, F.R.C.S. Preventing PCO ESCRS Ridley Medalist David Spalton, F.R.C.S., St. Thomas Hospital, London, discusses current and future methods of PCO prevention T wo or 3 years ago, people thought that posterior cap- sular opacification (PCO) had become a thing of the past. Although it's less of a problem now, it's still a significant clinical issue, especially with regard to the use of premium lenses and ac- commodative lenses. PCO is one of the limiting factors in the use of these lenses. Patients with diffractive multifo- cal lenses are susceptible to very small amounts of PCO. Diffractive lenses divide the light into two foci, which means there's only about 40% of light in each focus; therefore, the patient needs all the light he or she can get. A bit of PCO knocks that down considerably. It's a problem for accommoda- tive lenses as well because when the bag fibroses, it seems to stop the lenses from moving. Of course you can't refill the capsular bag with an elastic polymer because it develops PCO, too. Lens design and surgical methods At the moment, PCO is a multifacto- rial problem. In order to prevent PCO, changes in IOL material and design as well as various surgical techniques and pharmacological methods to remove or destroy lens epithelial cells have been prescribed. A lens with a good, sharp square-edge profile is necessary to prevent PCO. My colleagues and I looked at the electromicroscopy of a lot of IOLs, and we saw that the edge profile varies. Some manufac- turers make good ones while others don't. That's an important point be- cause some lenses may be advertised as having a square-edge profile, but they're not all equally effective. Hydrophylic lenses have a poorer square-edge profile than those made of hydrophobic materi- als. We developed a technique to look at square edges with what's called environmental scanning mi- croscopy. You can look at a wet spec- imen in an electromicroscope in its natural state. We could image these lenses very clearly and measure the sharpness of the edge using dedi- cated software we developed. Another factor that's important in PCO prevention is having a 360- degree square edge barrier right around the optic. A lot of lens de- signs have a break in the barrier at the optic haptic junction and that allows cells to escape onto the poste- rior capsule. Everything in IOL de- sign is a balance of the pros and cons. If we're going to have a 360- degree square edge, it tends to mean the lens has to be slightly thicker, and that means we can't get it through as small of an incision size. On the other hand, if we want a lens for a very small incision, the down- side is we tend to get higher PCO. In terms of surgical methods of PCO prevention, making the capsu- lorhexis slightly smaller than the optic of the implant is important. Over 2-4 weeks after surgery, the capsule fibroses and that fibrosis pushes the lens back onto the poste- rior capsule and creates a mechani- cal barrier on the posterior edge of the lens where the square edge bar- rier is located. It forms a sort of pres- sure barrier to the migration of epithelial cells. In addition, if the rhexis is asymmetrical or off of the lens implant, we don't get the same efficacy in pushing the lens back against the posterior capsule. Dealing with lens epithelial cells There are also pharmacological methods of dealing with PCO, al- though fundamental problems have been associated with many of them. One of the concepts involves lock- ing up the lens epithelial cells in the equatorial capsule. The surgeon per- forms a posterior capsulorhexis and prolapses the optic through that or uses what's called the bag-in-the- lens, a Belgian-designed lens. The rhexis has to be 5 mm in diameter, it has to be central, and there must be a concentric posterior capsulorhexis. The lens is placed so that both ante- rior and posterior rhexes lie in this groove in the lens, and these eyes maintain an entirely clear posterior capsule because there is no posterior capsule. However, a recent report by Liliana Werner, M.D., Ph.D., re- search associate professor, ophthal- mology and visual sciences department, John A. Moran Eye D espite advances in IOL design and surgical technique, poste- rior capsule opacification (PCO) continues to be a problem for cataract surgeons. Although the YAG laser is an easy, "miraculous" fix for patients with PCO, the rare creation of a retinal tear or detachment and the potential for per- manent post-YAG floaters makes its use less than ideal. A treatment that could eliminate PCO would help improve sur- gical outcomes and improve the chances of one day achieving an in- jectable crystalline lens substitute that could restore accommodation. In this month's column, David Spalton, F.R.C.S., reviews some of the issues and research that are ongoing in regard to reducing or potentially elimi- nating the occurrence of PCO. Richard Hoffman, M.D. Column Editor Cellular PCO Source: Mostafa A. Elgohary, M.D. Fibrotic PCO Source: Mostafa A. Elgohary, M.D. 44-51 Cataract_EW February 2011-dl2_Layout 1 2/4/11 2:20 PM Page 46

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