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Up Front | Jan 2009

Magnet-Driven Active-Shift IOL to Restore Accommodation

Magnets may improve the functionality of accommodating IOLs.

Today's available accommodating IOLs have failed to deliver the proof of concept of providing significant and reproducible anterior axial optic shift upon accommodative effort.1-3 While the 1CU (HumanOptics AG, Erlangen, Germany) showed some variable anterior shift,2 and the Eyeonics Crystalens AT-45 (Bausch & Lomb, Rochester, New York) exhibited a slight posterior shift corresponding to desaccommodation (Figure 1).1 In support, there was no statistical correlation between the unaided distance corrected near visual acuity and the optic movement as measured with dual-beam laser interferometry. Also, the broad-based flange haptics of these IOLs interfere with circumferential bending of the posterior capsule along the posterior optic edge,4 resulting in excessively high Nd:YAG laser capsulotomy rates. At 4 years, 36% of patients with the 1CU and 52% with the AT-45 Crystalens underwent capsulotomy (data on file).

How is the functional failure of these IOLs explained?

WORKING PRINCIPLES
The 1CU and the Crystalens rely on hypothetical working principles. The 1CU supposes that the evacuated capsular bag retains at least some of its elasticity, which allows contraction upon relaxation of the zonules. The Crystalens assumes that the vitreous is a noncompressible mass. As the ciliary muscle contracts and protrudes into the vitreous cavity, the vitreous body is displaced anteriorly, as is the optic in the capsular bag. The haptics of both accommodating IOLs shall maximize the resulting passive forward movement of the optic.

These working principles are pure conjectures that are not supported by the clinical reality that, in fact, the capsular bag shrinks significantly after cataract and IOL surgery due to fibrosis that distends and thus immobilizes the capsular-zonular diaphragm. The vitreous body increasingly disintegrates and regularly detaches during its lifetime, until it finally floats in a fluid-filled vitreous cavity.

Extensive fibrosis not only immobilizes the implant but may also result in deformation of the floppy haptics, which may be significant in some cases. With the 1CU, capsular contraction syndrome5 may occur; with the AT-45, Z-phenomenon6 may occur. The sometimes massive ingrowth and proliferation of lens epithelial cells (LECs) may also constrain the mobility of an implant. Thus, lack of passive mobility and the absence of an active driving force (Figure 2) explain the failure of the currently marketed single-optic accommodating IOL models to shift forward.

What can be done to make this principle work?

EXTENSIVE POLISHING
To study the impact of preserving as much of the capsular elasticity as possible, cataract surgery and Crystalens implantation was combined with extensive polishing of the anterior capsule. Sacu et al7 showed that removing the anterior LEC layer from the back of the residual peripheral anterior capsule significantly reduced fibrosis. A special aspiration curette was devised to achieve this.8 The additional treatment significantly influenced axial movement of the Crystalens optic; however, only the mean backward movement was reduced.

Thus, failure of extensive anterior capsular polishing to enable forward shifting of these accommodating IOLs demonstrates that the alleged working principles are purely hypothetical and do not mirror the clinical realities. Two prerequisites must be met to make the principle of single-optic accommodating IOLs work. First, contraction of the capsular bag with consecutive elongation of the zonules must be avoided to retain passive axial mobility of the IOL or capsule-implant-complex when the ciliary muscle contracts. Second, a constantly acting anterior vector force must be exerted on the implant or the capsular bag to drive the optic anteriorly when the relaxing zonules liberate the capsule-implant complex.

CONTACT-FREE MAGNETS
One way to achieve these prerequisites is using distance-acting, contact-free magnet forces. Preussner et al9 suggested the use of repulsive paired magnets implanted at the 3- and 9-o'clock positions. The magnets are integrated into a capsular tension ring (CTR) and beneath the superior and inferior rectus muscle insertion in special encasements. To preserve the individual capsular bag diameter, Preussner designed a special CTR with two overlapping paddles welded together following in-the-bag placement of the ring (ie, weldable CTR, or wCTR). The bevelled proximal edge of the overlying paddle and the underlying paddle are treated with overlapping argon laser spots (Figures 3 and 4).

A clinical study was planned in two steps. In the first study, ease of implantation, intraocular tolerance, feasibility of laser welding, and the resilience of laser welding against capsular shrinking were investigated. Also, the impact on anterior chamber depth and after-cataract formation were studied. Implementation of the magnets will be the object of the second step.

In the first phase, conducted by Dr. Menapace and his team at the Medical University of Vienna, eight eyes were implanted with the wCTR and an acrylic open-loop IOL.10 The rings were implanted either bimanually or with a special injector. Welding was performed the day after cataract surgery using a Goldmann 3-mirror lens (Haag Streit, Köniz, Switzerland) and a conventional blue-green argon laser. Welding was feasible in all cases, although exact positioning of the 0.2 mm in diameter was often demanding due to saccadic micro-movements of the eye.

Slit-lamp biomicroscopy and documentation of the relative position of the paddles by photography were performed at 1, 3, 6, and 9 months to test the durability of the welding. A dual-beam laser interferometer was used to determine the impact of implanting a wCTR with the paddles overlying the optic periphery on the anterior chamber depth (ACD), and the integrity of the optic edge barrier effect was followed with retroillumination photography.

RESULTS
Surgery was uneventful in all cases. The injector allowed well-controlled implantation of the wCTR through a 3.8-mm incision with minimal stress on the zonules. Postoperatively, the paddles were correctly positioned on top of the optic periphery. No intraocular irritation was noted. The welds appeared appropriate in position and intensity, although it was difficult to prove in some cases.

Durability. In most cases, the welds resisted the contraction forces of the capsular bag. In three eyes, however, the fibrotic forces resulted in breakage of the welds and some minor displacement of the paddles (Figure 5).

Anterior chamber depth. Mean ACD was 5.1 mm and 4.1 mm with and without the wCTR, respectively.

Barrier effect. At year 1, migrating equatorial LECs were halted at the optic edge in all cases. At 2 years, LEC migration requiring laser capsulotomy was observed in two cases.

DISCUSSION
Implantation of a wCTR was easy and safe, and welding was feasible in all cases and durable in most. At 2 years, the barrier function of the posterior optic edge was still preserved in most cases. The increase in ACD augments the potential for shift accommodation (preload) by approximately 1.00 D for a 20.00 D IOL.

The main problem with use of the wCTR is occasional failure of laser welding. Contraction of the capsular bag may exert significant traction on the zonules, and thus, loss of passive axial mobility of the lens-capsule complex. This may be due either to inappropriate placement of the welds or to excessive fibrotic contraction forces of the anterior capsule.

Fibrotic distension of the capsule diaphragm, however, is antagonized by extensive polishing of the anterior capsule, thereby removing the anterior LECs, which are the substrate for fibrotic contraction7,8 (Figure 6). The welds may then be resilient enough to withstand residual contraction forces.

Delayed barrier failure at the optic edge may eventually occur with any IOL, especially acrylic models.4 However, capsular fusion is compromised in the area where the paddles overlie the optic edge, similarly to what is observed with broad-based, one-piece IOLs. Due to the posterior displacement of the optic, the barrier failure rate may still be lower than with current single-optic–shift IOLs because the more posteriorly positioned optic presses its posterior edge against the posterior capsule.11 This may also partly compensate for the inherent weakening effect of anterior capsule polishing on collagenous capsular sealing and thus the barrier effect12 (Figure 7). Additionally, central posterior capsular opacification can be counteracted by adding a posterior capsulorrhexis.

FUTURE PERSPECTIVES
After we investigate the impact of additional capsule polishing and posterior capsulorrhexis, tolerance and functionality of adding the paired magnets to the paddles and beneath the superior and inferior rectus muscle insertions (Figure 8) will be evaluated. Upon accommodation, mobility of the IOL-bag diaphragm can then be exactly measured with laser interferometry, as previously done with passive-shift accommodating IOLs. The paddles are designed with a predetermined breaking line at the base, allowing secondary removal with the magnets in the unlikely case the patient should require MRI brain scans.

A possible alternative is to combine this magnet-driven principle with optic entrapment into a primary posterior capsulorrhexis (posterior optic buttonholing;13,14 Figure 9). This surgical technique not only excludes retrolental opacification, but it also reduces peripheral fibrosis to a minimum when combined with anterior capsule polishing. Mounting the magnets directly to the periphery of the IOL optic itself would also reduce the bulk of the IOL-capsule diaphragm. Altogether, this may further enhance the functionality of the system and exclude barrier failure and thus the need for Nd:YAG-laser capsulotomy.

In conclusion, the approach of adding magnets as the driving force may make axial-shift accommodating IOLs finally function. However, retaining the passive mobility of the capsule-IOL complex by preserving the individual capsular bag diameter and the primary tension of the zonules are key prerequisites to make this principle work.

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 e-mail: rupert.menapace@meduniwien.ac.at.

Paul-Rolf Preussner, MD, PhD, practices with the University Clinic Mainz, Germany. Professor Preussner states that he has a patent for the weldable CTR. He may be reached at e-mail: pr.preussner@uni-mainz.de.

  1. Koeppl C, Findl O, Menapace R, et al. Pilocarpine-induced shift of an accommodating intraocular lens: AT-45 Crystalens. J Cataract Refract Surg. 2005;31:1290-1297.
  2. Findl O, Kriechbaum K, Menapace R, et al. Laserinterferometric assessment of pilocarpine-induced movement of an accommodating intraocular lens: a randomized trial. Ophthalmology. 2004;111:1515-1521.
  3. Menapace R, Findl O, Kriechbaum K, Leydolt-Koeppl Ch. Accommodating intraocular lenses: a critical review of present and future concepts. Graefes Arch Clin Exp Ophthalmol. 2007;245:473-489.
  4. Menapace R. Prevention of after-cataract. In: T Kohnen, DD Koch, eds. Cataract and Refractive Surgery. Series Essentials in Ophthalmology; Springer; New York; 101-122.
  5. Menapace R. After-cataract following intraocular lens implantation. Part I. Genesis and prevention by optimizing conventional lens implants and surgical techniques. Ophthalmologe. 2007;104:253-262.
  6. Yuen L, Trattler W, Wachler BSB. Two cases of Z syndrome with the Crystalens after uneventful cataract surgery. J Cataract Refract Surg. 2008;34:1986-1989.
  7. Sacu S, Menapace R, Wirtitsch M, Buehl W, Kriechbaum K. Effect of anterior capsule polishing on fibrotic capsule opacification: three-year results. J Cataract Refract Surg. 2004;30:2322-2327.
  8. Preussner PR, Wahl J, Gerl R, Kreiner C, Serester A. Accommodative lens implant. Ophthalmologe. 2001;98:97-102.
  9. Vock L, Menapace R. Long-term YAG laser capsulotomy and after-cataract rates with the sharp edge Acrysof and round edge PhacoFlex intraocular lenses: 10 year results. Paper presented at: XXVth Congress of the ESCRS; September 8-12, 2007; Stockholm, Sweden.
  10. Menapace R. Pre-loaded shift IOL systems: Concepts and first clinical experiences. Paper presented at the: Annual Meeting of the DGII; February 18-19, 2005; Magdeburg, Germany.
  11. Nagamoto T, Fujiwara T. Inhibition of LEC migration at the IOL optic edge: role of capsule bending and contact pressure. J Cat Refract Surg. 2003;29:1605-1612.
  12. Menapace R, Wirtitsch M, Findl O, Buehl W, Kriechbaum K, Sacu S. Effect of anterior capsule polishing on posterior capsular opacification and Neodymium-YAG capsulotomy rate: a three-year randomized trial. J Cataract Refract Surg. 2005;31:2067-2075.
  13. Menapace R. Routine posterior optic buttonholing for eradication of posterior capsule opacification in adults - report of 500 consecutive cases. J Cataract Refract Surg. 2006;32: 929-943.
  14. Menapace R. Posterior capsulorhexis combined with optic buttonholing: an alternative to standard in-the-bag implantation of sharp-edged intraocular lenses? A critical analysis of 1000 consecutive cases. Graefes Arch Clin Exp Ophthalmol. 2008;246:787-801.

Jan 2009