Role of Capsular Tension Rings in Preventing Capsule Contraction

Capsule contraction syndrome remains a concern in phacoemulsification and posterior chamber intraocular lens (IOL) implantation. Clinically, capsule contraction may reduce the size or change the shape of the capsulorhexis after cataract surgery, and contraction forces may cause IOL decentration. In an effort to reduce this contraction, capsular tension rings have been implanted. The capsular tension ring has been demonstrated in vitro1 and in vivo2 over a short term to maintain the circular contour of the capsular bag and to provide additional support to the bag by pushing the bag's equator to a maximally extended position. This function of the capsular tension ring may also help to prevent capsule contraction and IOL decentration. Recently, Faschinger and Eckhardt3 reported 2 cases of complete capsulorhexis opening occlusion following cataract extraction and silicone IOL implantation. Because of presumed weak zonules (considering advanced age and pseudoexfoliation), the authors implanted capsular tension rings in these 2 cases during the surgery. This article draws readers' attention to the possibility that capsular tension rings may not resist capsule shrinkage. Furthermore, the rings may be unable to prevent occlusion of the capsulorhexis opening. Before addressing this issue, we would like to review the principle and mechanism of this occlusion, as well as the benefits of capsular tension rings in cataract surgery. Pathological studies4,5 show that lens epithelial cells (LECs) proliferate on the inner surfaces of the shrunken anterior capsule. The outgrowth of this membrane is from the margin of the anterior capsule centripetally and centrifugally toward the center of the anterior capsule opening. Therefore, the reason for occlusion of the capsulorhexis opening is not only the excessive shrinkage of the capsule but also the contraction of massive proliferation of metaplastic LECs acting against weak zonular support. Several benefits of the capsular tension ring in cataract surgery have been suggested.1,2,6,7 A capsular tension ring (1) appears to stabilize the capsule and enhance safety and efficacy during phacoemulsification and posterior chamber IOL implantation; (2) maintains the circular contour of the capsular bag and avoids collapse of the bag once the lens is removed from the capsule during surgery; (3) provides additional support to the bag by pushing the bag equator to the original position or beyond, which may help to prevent IOL decentration and capsule contraction in weak zonule or capsule fibrosis cases; (4) may inhibit LEC migration to the posterior capsule by physical compression and barrier function, which may reduce the incidence of a secondary cataract, especially if the ring has 90 degree edges for more barrier function.7 Previous studies8,9 have shown that the capsule contraction rate is significantly greater in eyes with silicone IOLs or plate-haptic silicone IOLs. The authors suggest that a single-piece poly(methyl methacrylate) lens with resistant haptics may produce stronger resistance than plate-haptic IOLs and caution against the use of silicone IOLs in eyes with a high risk of capsule contraction. Based on current knowledge and our clinical experience, we believe that capsular tension rings, when placed in-the-bag, provide a stronger and more evenly distributed resistance force in all directions of the capsule equator than the IOL haptics. This function of the capsular tension ring should help to prevent capsule contraction. This theory is supported by a recent study by Gonzalo Munoz, MD, and coworkers, which showed that capsular tension rings appear to provide an effective means of reducing anterior capsule contraction after cataract surgery in eyes with pseudoexfoliation (R. O'hEineachain, “Tension Rings Reduce Capsule Contraction, Spanish Study Shows,” EuroTimes, November–December 1999, page 32). However, implanting a capsular tension ring does not necessarily eliminate occlusion of the capsulorhexis opening, particularly when plate-haptic silicone IOLs are used in high-risk situations. The outgrowth of a new membrane and proliferation of LECs from the margin of the anterior capsulorhexis also play an important role in causing capsule contraction and occlusion of the opening.4,5 The opened capsular tension ring may not provide enough tension against capsule contraction forces in some situations, and consequently the capsular tension ring could collapse, which may eventually result in closure of the capsulorhexis opening. Therefore, designing a closed and foldable capsular tension ring with stronger material or an open ring that can be locked after insertion in the eye may help to solve this problem. Clinically, capsule contraction is often seen in eyes with weakened zonules from trauma, pseudoexfoliation, or when associated with inflammation such as uveitis. These conditions may trigger or promote capsule contraction following cataract surgery. Therefore, we still believe that implanting a capsular tension ring before or after phacoemulsification may reduce the incidence of capsule contraction in these situations. We agree with Drs. Faschinger and Eckhardt that additional studies are warranted and that patients at risk for capsular contraction should be followed carefully. Howard V. Gimbel MD, MPH Ran Sun MD aCalgary, Alberta, Canada