After-cataract formation is the most frequent complication following cataract surgery. Central posterior capsular opacification (PCO) is still an unsolved problem that requires laser treatment, and Nd:YAG laser capsulotomy is costly and not readily available for all patients—especially those living in developing countries. Conversely, even in industrialized countries, the diagnosis and treatment of after-cataract may be delayed, as elderly patients are often unable to regularly consult an ophthalmologist.
The main cause of an after-cataract formation occurs when equatorial lens epithelial cells (LECs) migrate and form pearls. In principle, there are two ways to prevent opacification of the visual axis by LECs: LEC removal or inhibition of LEC migration. Due to inadequate selectivity, LEC eradication by a chemical or immunologic agent has not yet attained clinical application. This method of LEC removal is controversial, as it may weaken zonular attachment to the lens capsule. Mechanical abrasion or capsular polishing by curettes mainly target the anterior LEC population. Although it significantly reduces anterior capsule fibrosis and its sequelae, abrasion or polishing drastically increases the subsequent need for Nd:YAG laser capsulotomy.1 This is due to the interference with collagenous sealing of both capsules along the optic rim, which is provided by the anterior LECs when they undergo myofibroblastic differentiation upon optic contact.2 The capsular leaves, even when primarily fused, may then be easily separated by the mechanical forces of a Sömmering's ring. Thus, the equatorial LECs, which are hardly reached by curettes, may resume migration and overcome the weakened optic edge barrier.
SHARP OPTIC EDGE OFTEN FAILS
Sharp-edged optics have significantly reduced the need for Nd:YAG laser capsulotomy; however, this concept does have its shortcomings. The required circumferential capsule-optic overlap, which reduces the free optic zone due to fibrotic whitening, may lead to excessive or asymmetric capsular contraction or retraction with consecutive optic tilt or decentration. A long-term retrospective evaluation (10 years) revealed that Nd:YAG laser capsulotomy rates with the most widely used hydrophobic acrylic IOL were as high as 42%.3 This is attributed to the delayed barrier failure at the optic edge that follows the redivision of once-fused peripheral capsules as the Sömmering's ring forms (Figure 1). Therefore, the barrier effect of a sharp posterior optic edge is often transient and may only delay the necessity to perform Nd:YAG laser capsulotomy in a considerable percentage of eyes.
A primary posterior capsulorrhexis adds a second barrier of defense, because it removes the central posterior capsule. The residual peripheral posterior capsule may still be opacified; however, it will result in a significant reduction of the free optic zone. Additionally, LECs may use the posterior optic surface as an alternate scaffold. Partial or total closure of the capsulorrhexis opening may, therefore, finally ensue (Figure 2).
Implementing a capsular bend within the capsular bag equator—by additionally implanting a capsular bending ring—significantly reduces after-cataract formation behind as well as outside an IOL,4 but it still does not fully prevent PCO formation. Limited efficacy and additional costs have prevented its widespread use.
Combining a posterior capsulorrhexis with posterior buttoning-in of the optic has been described for pediatric cases,5,6 and its long-term efficacy was proven in a clinical series.7 Because the posterior capsule lies on top of the IOL optic after buttonholing, the migrating LECs are deviated anteriorly (Figure 3). When bypassing the optic edge, LECs can no longer access the retrolental space, making after-cataract formation impossible.
In a large prospective clinical trial, posterior optic buttonholing (POBH) was applied in adults to elucidate its potential as a routine procedure. Since October 2004, more than 1,000 patients have been recruited. The technique has been previously described in detail.8
After lens removal, the posterior capsule is flattened with Healon (Advanced Medical Optics, Inc., Santa Ana, California) and centrally punctured with a 30-gauge hypodermic needle. The Utrata forceps (Duckworth & Kent, Ltd., Hertfordshire, England) are used to take up the capsule, and a well-centered opening (4–5 mm) is formed. The next step is crucial: Healon is again used to circumferentially separate the anterior hyaloid membrane from the residual posterior capsule, up to the periphery. Then, an open-loop IOL is injected into the residual capsular bag fornix. The Hoya AF-1 IOL (Hoya, Frankfurt, Germany) is preferred, due to its haptic junction design (Figure 4). Once in the bag, the optic is buttoned-in by gently pressing down (Figure 5). The Healon is aspirated from the anterior chamber, and the incision is left unsutured. Topical anesthesia is used throughout the procedure.
Approximately 150 eyes underwent anterior capsule polishing with a special LEC aspiration curette (Figure 6) to elucidate the potential profit of such an additional procedure.9 It was performed after completing the cortex aspiration and peeling residual lens fibers adhering to the posterior capsule. The additional time required was 1.5 minutes.
The POBH technique is well controlled and safe. Because the haptics reside within the capsular equator, all optics automatically center, even within a suboptimally centered primary posterior continuous curvilinear capsulorrhexis opening (Figure 7). Vitreous complications were rare and mainly occurred in the initial series. Of the 1,000 cases, only one intraoperative and three postoperative cases of vitrectomy occurred. Of these, two were caused by secondary fibrotic retraction of the posterior capsulorrhexis from the optic edge. There was only one retinal detachment after 4 months (young male with high myopia), which was repaired. There were no cases of clinically significant cystoid macular edema.
The safety profile was determined in detail during specific prospective, randomized, bilateral studies comparing POBH with the standard in-the-bag technique. There was no significant difference in postoperative pressure rise10 and anterior chamber inflammation (laser cell-flare-metry).11 Macular thickness and morphology were examined with high-resolution optical coherence tomography; no difference was noted.12 With the same high-precision technology, axial position change and final position of the optic were measured. Other than after placement in the bag, the optic reached its final axial position immediately after the POBH procedure.13 With no optic shift, glasses can be immediately prescribed. Because the optic positions itself approximately 1 mm more posteriorly than after bag placement (Figure 8), the vitreous body is stabilized, which may explain the low incidence of retinal complications. An ongoing study showed excellent autocentration capabilities of the Hoya AF-1 IOL.
The retrolental space remained completely clear in all cases. This is not surprising, as by principle the anteriorly deviated LECs can no longer gain access to the space. Also, fibrotic whitening and contraction of the anterior capsule was significantly reduced. Direct contact is prohibited where the posterior capsule is sandwiched between the optic and anterior capsule. Consequently, the contact-mediated myofibroblastic transdifferentiation of the anterior LECs on the backside of the anterior capsule is not initiated. Only at the areas inside the haptic junction can the anterior capsule still contact the optic and thus cause opacification (Figure 9). From there, limited migration of anterior LECs may be seen in the capsulorrhexis rim of the neighboring anterior, and occasionally also into the posterior capsule.
In polished eyes, residues of capsular fibrosis have not been observed, thus preserving the full transparency of the whole optic (Figure 10). Alternately, making the anterior capsulorrhexis larger than the optic diameter precludes optic contact adjacent to the haptic junction, and thus fibrosis of the anterior capsule. This may be difficult to perform. More importantly, it excludes the option of sulcus positioning and posterior buttonholing of the optic through an anterior 5-mm continuous curvilinear capsulorrhexis, should the primary posterior continuous curvilinear capsulorrhexis happen to be too large or eccentric to create a tight diaphragm around the optic. With a posterior capsulorrhexis opening that evades the optic rim, secondary vitreous herniation may ensue due to continuous saccadic eye movements. This may also occur with a posterior capsulorrhexis that is only scarcely overlapping the optic rim, because it may be secondarily enlarged by the fibrosis arising from an anterior capsulorrhexis that is larger than the optic. Therefore, polishing of the anterior capsule is highly preferred.
SAFE AND EFFECTIVE ROUTINE PROCEDURE
In conclusion, primary posterior continuous curvilinear capsulorrhexis with optic buttonholing holds promise to become a viable option for routine cataract surgery. It is well controlled, safe, effective, and it completely and permanently avoids both regeneratory and fibrotic after-cataract formation behind the optic. The optic is inherently significantly reduced. Additional capsular polishing is recommended to fully eradicate any residual fibrotic changes. For this purpose, a special aspiration curette has been made available,9 allowing efficient and safe anterior lens epithelial cell debridement.
Rupert Menapace, MD, is a Professor of Ophthalmology and Head of the Intraocular Lens Service, Medical School of Vienna, Austria. Professor Menapace states that he has no financial interest in the products or companies mentioned. He may be reached at firstname.lastname@example.org.