Cataract surgery is the most common operation performed by ophthalmologists. Although it has a very high success rate, certain complications may occur. Intraocular lens (IOL) malpositions range from simple IOL decentration to luxation into the posterior segment. Subluxated IOLs involve such extreme decentration that the IOL optic covers only a small fraction of the pupillary space. Luxation involves total dislocation of the IOL into the posterior segment. Decentration of an IOL may be the result of the original surgical placement of the lens, or it may develop in the postoperative period because of external (eg, trauma, eye rubbing) or internal forces (eg, scarring, peripheral anterior synechiae [PAS], capsular contraction, size disparity). Posterior dislocation of an intraocular lens (IOL) is an uncommon complication of cataract surgery and Nd:YAG posterior capsulotomy.
See What the Eyes Tell You: 16 Abnormalities of the Lens, a Critical Images slideshow, to help recognize lens abnormalities that are clues to various conditions and diseases.
IOL dislocation can be subdivided into early and late dislocation. Early dislocation refers to dislocation occurring within 3 months of cataract surgery, whereas late dislocation occurs more than 3 months after cataract extraction. 
Posterior dislocation of an IOL may occur during or shortly after cataract surgery. In these cases, posterior capsular rupture or zonular dialysis usually is present. It occurs because of improper fixation within the capsular bag and instability of the IOL–capsular bag complex.  The implementation of a continuous curvilinear capsulorrhexis (CCC) during phacoemulsification has decreased the rate of early IOL dislocation.  CCC gives support to the IOL optic for 360 degrees and permits excellent IOL fixation. Prior to CCC, most IOL dislocation occurred secondary to asymmetric IOL fixation or IOL malposition within the capsular bag. Rarely, it may occur following Nd:YAG capsulotomy or beyond the immediate postoperative period. Trauma may be a precipitant in these cases.
Late IOL dislocation has been noted to occur more frequently than previously thought. [1, 4, 5] Late IOL dislocation results from zonular weakness since the IOL is adequately fixed within the capsular bag. Several risk factors, including pseudoexfoliation syndrome,  trauma, prior vitreoretinal surgery, and connective tissue disorders, have been associated with zonular weakness. In a retrospective case series of 86 late IOL dislocations, the IOL dislocated on average 8.5 years after phacoemulsification and IOL implantation.  These same authors reported that patients with any type of IOL were at risk for late in-the-bag IOL dislocation. A population-based study of patients by Pueringer et al found that after cataract extraction, the long-term risk of late IOL dislocation was low and had no significant change over the almost 30-year study period. 
The IOL rarely dislocates completely onto the retinal surface. It usually lies meshed into the anterior vitreous with one haptic still adherent to the capsule or iris. It may cause a vitreous hemorrhage by mechanical contact with ciliary body vessels. The IOL may be related to retinal detachment or cystoid macular edema secondary to vitreous changes and may cause pupillary block or corneal contact with secondary corneal edema. On many occasions, it does not cause any complications and may be left alone if the patient is able to use aphakic spectacles or contact lenses.
Clinically insignificant decentration occurs in at least 25% of cases. Clinically significant decentration occurs in about 3% of the cases. The frequency of IOL dislocation ranges from 0.2-1.8%. The rate is lower in eyes with posterior chamber IOLs (PCIOL) than with anterior chamber IOLs (ACIOL) or iris-supported lenses. However, since posterior chamber IOLs constitute most lenses implanted, decentered and dislocated posterior chamber IOLs have become more prevalent.
The frequency appears to have increased in the past few years because of the following reasons: (1) phacoemulsification has a steep learning curve, and, as it becomes more popular, more complications are occurring; (2) anterior segment surgeons are becoming more reluctant to place anterior chamber intraocular lenses (ACIOLs); (3) aggressive placement of posterior chamber IOL in the presence of capsular tears has become more common; and (4) silicone plate IOLs have become popular.
A longitudinal study reported that, in 85% of posterior chamber IOL exchange cases, the indication was decentration/dislocation of the lens.
Pseudoexfoliation syndrome, by virtue of its weakening effect on the zonules, is one of the most common conditions associated with late IOL dislocation.  The pseudoexfoliation syndrome is commonly seen in people with Scandinavian heritage.
No gender preference exists in IOL dislocation.
Age is not related to this condition.
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