The Opacifying Capsule: Can We Win The Battle?
The Opacifying Capsule: Can We Win The Battle?
The basics still hold true, but recent design upgrades warrant a rethinking of classic principles.
By Steven Dewey, MD
Advances in surgical technique depend on advances in technology, and vice-versa. While referring specifically to the reduction of PCO, Dr. David Apple first encapsulated our current surgery some 20 years ago. His six steps1 still remain true—a square-edged IOL of proper material placed in a capsule hydrodissected free of cortical remnants with complete edge coverage by the capsulorhexis maximizes capsule contact and reduces the incidence of PCO. He felt that cortical clean-up and IOL edge design were the keys.
When these steps were first outlined, capsule opacification was still a bit of a mystery. The differences between early opacification, occurring due to LEC migration within the first several months, and late opacification, due to cortical regeneration years later, were not understood. The advent of the Alcon MA60BM (the three-piece, 360-degree square edged hydrophobic acrylic lens) allowed Dr. Apple to make his observations. Early-phase PCO was virtually eliminated by this IOL, and ushered us into our current generation IOL designs.
One Step Forward, One Step Back
As a result, virtually all current-generation IOLs incorporate a PCO-reducing edge. The edge design alone, however, does not mean that an IOL will reduce PCO to the same degree as another IOL with a similar edge. Microincision cataract surgery (MICS) requires lenses that obviously are designed to be inserted through small incisions. While retaining some of the features of larger IOLs, MICS lenses are thinner and more flexible. Schriefl and Menapace reported higher levels of PCO with the Bausch + Lomb Akreos MI60 compared to the Hoya iMICS Y-60H.2 Cleary et al.3 compared the single-piece hydrophilic acrylic HumanOptics MC611MI to the three-piece hydrophobic acrylic MA60AC. Reduced resistance to PCO in the MC611M was identified as early as three months. The authors of both studies posit that the thick optichaptic junction prevents 360-degree capsule bend formation and allows LECs to migrate unopposed across the posterior capsule.
The hydrophilic nature of the IOL may be as much a culprit. In a study comparing double-square edged optics, Iwase et al.4 found increased levels of PCO with the Meridian HG60M (B+L) when compared to the SA60AT (Alcon). Alternatively, MICS surgery requires smaller incisions with smaller instrumentation. Inherently, these instruments have limitations not found with larger incisions. Oar-locking, for instance, occurs when an instrument too-tightly fits an incision, and limits the mobility of that instrument in the eye. Combine oar-locking with the decreased irrigation/aspiration throughput of the smaller instrument, and it is possible that cortical clean-up will suffer as our incisions shrink.
The Patient's Perspective
The newer premium IOLs, especially multifocal IOLs, require a clearer posterior capsule to function well.5 While providing significant functional convenience, these optic designs are at best a compromise to help patients achieve spectacle independence. After the light is split into separate points of focus, the quality of the image reaching the retina must be pristine for the patient to perceive the benefit. A mix of fibrosis and pearl formation, even as seen in early-phase PCO, can easily undo the best optic design.
This correlates with a recent study by Wakamatsu et al.,6 who found significant visual improvement after YAG capsulotomy in patients with mild PCO. Preoperatively, these patients had excellent Snellen acuity, yet demonstrated significant improvements following the procedure. While their study was limited to monofocal IOLs, spherical-like and higher-order abberations appear to have impacted low-contrast visual acuity, and reduction of these by capsulotomy provided the improvement in function.
Polishing Undoes the Result
Lens epithelial cells are not particularly active, until they respond to an injury such as cataract surgery. And they are quite resilient. They appear to have only two functions—repair or regeneration. Repair seems to be most associated with a fibrotic response and regeneration with pearl formation and Soemmering's ring. Studies designed to evaluate the reduction in PCO by reducing the volume of LECs have been fairly confounding. It would seem that every attempt made to lower the surviving LEC population—polishing, chemical ablation, etc.—results in increasing levels of PCO.7
An explanation for this paradoxical inconsistency may have been found. In a paired cadaver eye study, Liu et al.,8 performed cataract surgery and either polished the underside of the anterior capsule or left it unpolished. The capsules were then cultured, and LEC activity was monitored. In the unpolished capsules, LECs did not proliferate; rather, they died and left large, vacant patches. In the polished capsules, LECs demonstrated “robust” proliferation, appearing to migrate from regions where the polishing hadn't disrupted cell populations. In a separate, similarly designed study of living patients, the polished anterior capsules were much clearer at a year than the unpolished capsules, but no effect could be seen on PCO by that early stage. The authors speculate that their contradictory laboratory finding explains the variability in PCO response in studies involving capsule polishing.
Late-Stage PCO: Round-edged Silicone Wins?
While the six rules remain relatively intact, Vock et al. have found that a round-edged silicone IOL (the SI-40) actually outperformed the square-edged IOL (the AR40e) in prevention of PCO at the 10-year mark.9 It really wasn't even close—patients receiving an SI-40 had an 18% chance of requiring a YAG capsulotomy, while those with an AR40e had a 42% chance. That's almost 2.5 times the risk for a square-edged hydrophobic acrylic IOL compared to a round-edged silicone IOL. Goes against conventional wisdom, doesn't it?
While the magnitude of the difference is surprising, the PCO-reducing qualities of the SI-40 aren't. First, the three-piece design allows for the capsule to appose across the entire optic edge. Second, the silicone optic induces early fibrous metaplasia of the LECs on the anterior capsule, creating a secure capsule bend along the optic edge. Third, while the corners of the edge of the IOL are rounded, the edge of the IOL itself is a flat vertical surface. This combination of factors leads to a fibrous capsular bend resilient enough to resist the regeneration of cortex and the formation of Soemmering's ring.
Cadavers Have No Secrets (or “Dead Men Tell No Tales”)
Lastly, a bit of good news for the users of single-piece hydrophobic acrylic IOLs. Evaluating the pathology of cadaver eyes containing these lenses (Alcon Acrysof series single-piece), Ness et al.10 found no difference in central or peripheral PCO formation compared to similar post-implantation age three-piece hydrophobic acrylic IOLs. While previous clinical studies have demonstrated a short-term increase in the likelihood of PCO formation with these single-piece lenses,11 this observational study showed that the posterior square edge maintains a strong barrier against late regenerating cortex. As expected, when the single-piece IOL did relent to PCO, the point of cellular migration was typically the broad optic-haptic junction.
The past decade has seen amazing advancements in improving outcomes for patients undergoing cataract surgery. New modalities for cataract removal allow for safer surgery through smaller incisions with faster recovery. IOL designs now correct for corneal abberations, astigmatism and even presbyopia. While the femtosecond laser promises to standardize the surgical outcome, the next forefront of IOL design will undoubtedly include custom-sized IOLs.
No matter how sophisticated these advances seem, they remain susceptible to simple PCO. The battle persists. OM
1. Apple DJ, Peng Q, Visessook N, et al. Eradication of posterior capsule opacification. Documentation of a marked decrease in Neodymium: Yttrium-Aluminium-Garnet laser posterior capsulotomy rates noted in an analysis of 5416 pseudophakic human eyes obtained postmortem. Ophthalmology 2001; 108: 505–518.
2. Schriefl S, Menapace R. Intraocular lenses for micro-incision cataract surgery - 2 year results; Bausch & Lomb Akreos MI60 vs. HOYA iMICS Y-60H. ESCRS 2011 Vienna.
3. Cleary G, Spalton DJ, Hancox et al. Randomized intraindividual comparison of posterior capsule opacification between a microincision intraocular lens and a conventional intraocular lens. J Cataract Refract Surg. 2009 Feb;35(2):265-72.
4. Iwase T, Nishi Y, Oveson B, Young-Joon J. Hydrophilic versus double-square-edged hydrophilic foldable acrylic intraocular lens: Effect on posterior capsule opacification. J Cataract Refract Surg. 2011 June: 37(6) 1060-1068.
5. de Vries NE, Webers CA, Touwslager WR, Bauer NJ, de Brabander J, Berendschot TT, Nuijts RM. Dissatisfaction after implantation of multifocal intraocular lenses. J Cataract Refract Surg. 2011 May;37(5):859-65. Epub 2011 Mar 11.
6. Wakamatsu TH, Yamaguchi T, Negishi K, et al. Functional Visual Acuity after neodymium:YAG laser capsulotomy in patients with posterior capsule opacificatin and good visual acuity preoperatively. J Cataract Refract Surg: 2011 Feb 37 (2) 258-264.
7. Bolz M, Menapace R, Findl O, et al. Effect of anterior capsule polishing on the posterior capsule opacification-inhibiting properties of a sharp-edged, 3-piece, silicone intraocular lens: three- and 5-year results of a randomized trial. J Cataract Refract Surg. 2006;32(9):1513-1520.
8. Liu X, Cheng B, Zheng D, et al. Role of anterior capsule polisihing in residual lens epithelial cell proliferation. J Cataract Refract Surg: 2010 Feb 36 (2) 208-214.
9. Vock L, Menapace R, Stifter E, Georgopoulos M, Sacu S, Bühl W. Posterior capsule opacification and neodymium:YAG laser capsulotomy rates with a round-edged silicone and a sharp-edged hydrophobic acrylic intraocular lens 10 years after surgery. J Cataract Refract Surg. 2009;35(3):459-465.
10. Ness P, Werner L, Maddula S, et al. Pathology of 219 human cadaver eyes with 1-piece or 3-piece hydrophobic acrylic intraocular lenses: Capsular bag opacifiction and sites o fsquare-edged barrier breach. J Cataract Refract Surg 2011 May: 37 (5) 923-930.
11. Mian SI, Fahim K, Marcovitch A, Gada H, Musch DC, Sugar A. Nd:YAG capsulotomy rates after use of the AcrySof acrylic three piece and one piece intraocular lenses. Br J Ophthalmol. 2005 November; 89(11): 1453-1457.
||Steven Dewey, MD, is a private practice ophthalmologist in Colorado Springs, and a consultant to AMO. He can be reached at firstname.lastname@example.org.|
Ophthamology Management, Issue: October 2011