Devices designed to help stabilize the loosened capsular bag during phacoemulsification include (1) capsular tension rings (CTRs; Morcher GmbH, Stuttgart, Germany, and Ophtec, Groningen, the Netherlands), (2) the Ahmed capsular tension segment (Morcher GmbH), and (3) capsule retractors such as the Mackool Cataract Support System (Duckworth & Kent Ltd., Hertfordshire, England, and Impex, Staten Island, New York). Thanks to these devices and to techniques such as phaco chop, surgeons are frequently able to preserve the capsular bag, despite the multiple challenges posed by weakened zonules. The surgeon, however, is then faced with a new set of decisions. Is the capsular bag suitable for the long-term support of an IOL? Which IOL should be used? Is a CTR or other implantable device, such as a Cionni modified CTR (Morcher GmbH), necessary? The same questions must be considered for all eyes with pseudoexfoliation (PXF) in light of the increasing incidence of late spontaneous dislocation of the capsular bag.1-3
SPONTANEOUS DISLOCATION OF THE CAPSULAR BAG
At the 2000 Annual Meeting of the American Academy of Ophthalmology, Mamalis et al1 reported their initial series of nine patients with PXF who presented with late spontaneous dislocation of the capsular bag. These dislocations occurred between 5 years and 10 years after the original surgery. The investigators' case series comprised eight PMMA IOLs and one plate haptic silicone IOL, and it was published in Ophthalmology 1 year later.2 I reported on two cases of spontaneous dislocation in PXF patients with three-piece silicone IOLs.3 Typically, there is a fibrotic and contracted capsulorrhexis in these dislocated bag-IOL cases. Exaggerated contraction of the capsulorrhexis is usually an indication of weak zonules.4-6 It also seems likely, however, that capsulophimosis and extensive anterior capsule fibrosis exerted excessive centripetal strain on the already weakened zonules in these eyes.
Given that the capsulorrhexis technique was not widely adopted until the early 1990s, and considering the 5- to 10-year latency for this complication, it makes sense that we surgeons are seeing an increasing frequency and growing awareness of this complication. In assessing the risk of delayed spontaneous bag dislocation in PXF, however, what is not known is the denominator. Complicating any evaluation of preventive measures is the fact that dislocation may take more than 10 years to occur. Nonetheless, I believe it is possible to make rational choices based upon our current knowledge of IOL design and materials.
CTRs AND PXF
Does every patient with PXF require a CTR? This decision is controversial, and the extent of zonular deficiency should be a determinant. Significant zonular weakness would certainly be a reasonable indication for a CTR. Many PXF patients, however, exhibit no intraoperative evidence of zonular laxity, and I do not think that a CTR is necessary in such cases. Nevertheless, there are several surgical and IOL design objectives that make sense for any patient with PXF.
Thorough cortical clean-up is especially important in PXF eyes. Although the circumferential anterior capsular overlap of the optic edge is desirable, an excessively small-diameter capsulorrhexis must be avoided in these patients. IOLs with optic diameters smaller than 6 mm should generally be avoided for this reason. Following IOL implantation, a small capsulorrhexis can be secondarily enlarged if necessary. After obliquely cutting one edge with a long Vannas scissors, I retear the opening under viscoelastic.
Because hydrophobic acrylic IOLs are associated with less anterior capsular fibrosis when compared with silicone lenses,7,8 I believe that the former material is preferable for PXF eyes. Three-piece lens designs with broad stiff PMMA haptics are able to exert the maximum centrifugal tension against the capsular fornices.
They are preferable to the soft, floppy, single-piece haptics for this reason. Because of their haptic design and higher tendency for anterior capsular fibrosis, one should probably avoid silicone plate haptic IOLs in PXF eyes. Finally, one should specifically examine the anterior capsular reaction at the final 1-month postoperative visit in patients with PXF. If there already are signs of early contracture and fibrosis, prophylactic Nd:YAG relaxing cuts in the capsulorrhexis edge should be considered.
In any eye where the surgeon notes intraoperative signs of zonular laxity, the placement of a CTR is prudent. The goals would be to (1) prevent capsulophimosis, (2) reduce centripetal zonular stress by resisting capsulorrhexis contraction, and (3) avoid IOL decentration caused by asymmetric capsular fibrosis. There are numerous situations, however, where a CTR alone might not afford sufficient long-term capsular support. Such cases include eyes with a large zonular dialysis or severe diffuse circumferential weakness. It is for these eyes that the Cionni modified CTR or the Ahmed capsular tension segment were designed.
If a CTR is not used, there are other options to consider. As an alternative to enlarging a small-diameter capsulorrhexis, one could make relaxing incisions in the capsulorrhexis edge after placing the IOL in the bag. With a temporal incision, I would orient the haptics along the horizontal axis (3- to 9-o'clock position) and make two opposing cuts in the capsulorrhexis edge superiorly and inferiorly (12- and 6-o'clock positions). The cuts should not extend too far peripherally, because they merely need to prevent the sphincter-like contraction of the capsulorhexis margin.
Finally, one could place the IOL in the sulcus. The sulcus diameter can be estimated by adding 1.5 mm to the white-to-white horizontal corneal diameter. Thus, the typical foldable IOL of 13 mm in overall length is too short for a corneal diameter of 12 mm or greater. STAAR Surgical Company (Monrovia, California) makes a 13.5-mm foldable silicone IOL (model AQ 2010 V) that is my preference for sulcus placement. The IOL power should be reduced by 0.50 D to 1.00 D from that calculated for capsular bag placement.9 The single-piece AcrySof (Alcon Laboratories, Inc., Fort Worth, Texas) is not only too short for sulcus placement, but it has thicker sharp-edged haptics that can cause pigment dispersion. If sulcus placement is elected because of a severe zonular dialysis, one should consider making multiple relaxing cuts in the capsulorrhexis edge to avoid extensive and asymmetric bag contracture with avulsion of the remaining hemisphere of weak zonules.
CONCLUSION
In conclusion, whereas excellent results can be obtained with a wide range of IOL materials and designs in routine cases, eyes with weak zonules are at greater risk for delayed IOL subluxation, dislocation, and capsulophimosis. Anterior capsule fibrosis and capsulorrhexis contraction should be minimized through a combination of surgical technique and IOL selection.
David F. Chang, MD, is Clinical Professor of Ophthalmology at the University of California, San Francisco. Dr. Chang states that he is a consultant to Advanced Medical Optics, Inc. and Alcon Laboratories, Inc., but states that he has no financial interest in any product or company mentioned. He is a member of the CRST Europe Global Advisory Board. Dr. Chang may be reached at +1 650 948 9123; dceye@earthlink.net.
Up Front | May 2007
IOL Selection for the Weakened Capsular Bag
Minimize anterior capsule fibrosis and capsulorrhexis contraction through a combination of surgical technique and IOL selection.
David F. Chang, MD
