EyeWorld Asia-Pacific June 2011 Issue

26 EW CATARACT/IOL June 2011 ESCRS Ridley Medalist David Spalton, FRCS, St. Thomas Hospital, London, discusses current and future methods of PCO prevention T wo or 3 years ago, people thought that posterior capsular 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 accommodative lenses. PCO is one of the limiting factors in the use of these lenses. Patients with diffractive multifocal 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 accommodative 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 multifactorial 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 manufacturers make good ones while others don’t. That’s an important point because 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 materials. We developed a technique to look at square edges with what’s called environmental scanning microscopy. You can look at a wet specimen in an Preventing PCO by David Spalton, FRCS Cellular PCO Fibrotic PCO Source: Mostafa A. Elgohary, MD electromicroscope in its natural state. We could image these lenses very clearly and measure the sharpness of the edge using dedicated 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 designs have a break in the barrier at the optic haptic junction and that allows cells to escape onto the posterior capsule. Everything in IOL design 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 downside is we tend to get higher PCO. In terms of surgical methods of PCO prevention, making the capsulorhexis 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 posterior capsule and creates a mechanical barrier on the posterior edge of the lens where the square edge barrier is located. It forms a sort of pressure 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. Views from Asia-Pacific Choun-Ki JOO, MD Professor, Department of Ophthalmology & Visual Science, Seoul St. Mary’s Hospital Eye Institute, College of Medicine, The Catholic University of Korea #505 Banpo-dong, Seocho-Ku, Seoul, 137-040, Korea Tel. no. +82-2-2258-7620 Fax no. +82-2-533-3801 ckjoo@catholic.ac.kr P osterior capsular opacity (PCO) or after-cataract is a complication which will be ongoing as long as we live in the surgical paradigm of inserting an IOL into the capsular bag. To prevent PCO, inventive research is being conducted into the material and shape of IOLs, pharmacologic agents, and instruments which inhibit or eliminate the lens epithelial cells themselves, but the most important emphasis in the practical field is the surgical management. As David [Spalton] said previously, the continuous curvilinear capsulorhexis (CCC) should be made as round as possible, along the limbal margin, a bit smaller than the optic diameter. In my opinion, removing completely the viscoelastic within the capsular bag should be considered as important as the accurate CCC to reduce the PCO. After inserting the IOL in the bag, the viscoelastic should be completely removed especially behind of the IOL, so that the posterior surface of the IOL can adhere closely to the posterior capsule. Although viscoelastic material remains within the bag, it usually disappears within 1-2 days, but this is sufficient for the lens epithelial cells to migrate or seed from the periphery to the center during that time. While we continue our work in searching for the ideal IOL material and design, and other ways to get rid of the lens epithelial cells, we must take care not to omit any part of the basic procedures of the surgery. Editors’ note: Prof. Joo has no financial interests related to his comments.