Intraocular lens dislocation

Dislocation: The act of displacing, or the state of being displaced. Cataract surgery with intraocular lens (IOL) implantation has evolved into highly successful surgery. However, IOL dislocations are among the most common complications following this surgery. The yearly ASCRS–ESCRS survey of foldable IOLs requiring explantation or secondary intervention analyzed at the University of Utah’s Intermountain Ocular Research Center has shown that dislocation/decentration was overall the most common reason for IOL explantation over the past decade.1,A It is interesting to note that IOL dislocation seems to occur in a bimodal distribution.2 Early IOL dislocation is usually secondary to improper fixation of the IOL within the capsular bag, issues with asymmetric IOL fixation, or an incomplete or torn capsulorhexis. Overall, the incidence of early IOL dislocation has decreased with the increased use of a continuous curvilinear capsulorhexis and improved phacoemulsification techniques, which allow complete removal of a cataract with secure placement of the IOL within the capsular bag. Late IOL dislocation is often associated with spontaneous IOL dislocation within the intact capsular bag, and the incidence of this complication has increased recently.3 These late dislocations are generally associated with conditions of zonular weakness rather than inadequate IOL fixation. A study of late in-the-bag spontaneous IOL dislocation from the Intermountain Ocular Research Center looked at 86 IOLs that were explanted within the capsular bag following spontaneous dislocation.3 The mean time from surgery to dislocation of the IOL was 8.5 years. The main conditions associated with this late spontaneous IOL dislocation were pseudoexfoliation (PXF) in 50% of the cases and prior vitreoretinal surgery in almost 20%. This late in-the-bag spontaneous dislocation occurred with many different IOL designs, as well as with different IOL materials. In this issue, Shingleton et al. (pages 984–993) present results of the surgical management of IOL dislocation in patients with pseudoexfoliation (PXF). They evaluated 81 eyes that had IOL dislocation. Ninety-one percent of the eyes had IOL–capsular bag complex dislocations, whereas only 9% had IOL dislocations alone. The mean time for dislocation following cataract surgery was 8.5 years. An IOL exchange was performed in 79% of the eyes and IOL repositioning in 21%. Various IOLs, including anterior chamber, scleral-sutured posterior chamber, and iris-sutured posterior chamber, were used for IOL exchange in these patients. Intraocular lens repositioning included suturing the IOL to the iris as well as to the ciliary sulcus using a lassoing technique. This large group of patients had no significant intraoperative complications using these techniques. The corrected distance visual acuity had improved in all eyes at the final follow-up examination at 2.5 years. In addition, the mean intraocular pressure (IOP) had decreased by 4.2 mm at the final follow-up examination and the mean glaucoma medication requirement remained stable. The authors found that patients with IOL dislocation and PXF have the potential for excellent visual outcomes with minimal intraoperative and postoperative complications. One important question to be asked is why PXF is noted so commonly in patients with late spontaneous IOL dislocation within the capsular bag. Pseudoexfoliation is characterized by zonular weakness in addition to a variety of other problems, including poor mydriasis and shallow anterior chamber, which may make the surgical procedure more difficult. More important, PXF may directly affect the zonular fibers and their attachment, weakening them significantly. Pseudoexfoliation material causes alterations of the origin and anchorage of the zonular fibers to the ciliary body by these PXF fibers. Second, the PXF material infiltrates the bundles of zonular fibers supporting the crystalline lens. Finally, the attachment of the zonular fibers to the lens capsule is weakened by the PXF material. These factors can ultimately lead to dehiscence of the zonule as well as overall instability of the IOL–capsular bag complex, which can lead to spontaneous IOL subluxation or dislocation. Several methods to prevent late spontaneous dislocation of IOLs in patients with PXF have been proposed. This includes the use of IOLs that have firm haptics to counterbalance progressive capsular bag phimosis and shrinkage. However, in pathologic analyses of these patients, the dislocation did not seem to be affected by different IOL designs or IOL materials. In addition, the use of capsular tension rings (CTRs) has been advocated in a prophylactic manner to prevent the spontaneous dislocation of the IOL–capsular bag complex in patients with PXF. However, no long-term prospective studies have been performed to confirm this contention. In addition, our laboratory has now analyzed dozens of IOLs that have spontaneously dislocated within the capsular bag despite the presence of a CTR. Spontaneous dislocation of IOLs within the capsular bag has been noted to occur a mean of 8.5 years following otherwise uneventful cataract surgery in 2 major studies. The greatest overall risk for this spontaneous occurrence is the presence of PXF. Fortunately, the surgical management of these patients has been successful, with overall improvement of visual acuity as well as decrease of IOP and stabilization of glaucoma medications.