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I read with interest the case report of Ashraff et al,1 where a posterior chamber phakic intraocular lens (PCPIOL) was used in a pseudophakic eye with axial myopia and pseudoexfoliation for the management of anisometropia. I would like to highlight a potential problem in such eyes: dislocation of PCPIOL into the vitreous cavity.
PCPIOLs are inserted blindly behind the iris and, depending on the design, allow their haptics to rest at the structures of the posterior chamber or float in it. Ultrasound biomicroscopy (UBM) identified haptic-zonules contact and lens rotation for the implantable contact lens (ICL)2 and the phakic refractive lens (PRL),3 although these PCPIOLs are intended to fixate at the ciliary sulcus and float in the posterior chamber respectively. Because of this potential haptic-zonules contact and lens rotation of PCPIOLs the entire zonular apparatus should be intact and healthy.
Pseudoexfoliation is characterised by progressive zonular disruption and axial myopia by zonular weakness and both conditions may lead to zonular defects. Although phakodonesis and iridodonesis may point towards zonular insufficiency, those signs may be absent in a number of eyes with occult zonular defects as shown in UBM studies.4 Such zonular defects may result in spontaneous dislocation of the PCPIOL into the vitreous cavity. Two cases have been described already where PCPIOLs dislocated into the vitreous cavity through such defects. Kaya et al5 reported a case of dislocation of a silicone PCPIOL into the vitreous cavity following mild head injury 3 weeks postoperatively in a highly myopic eye (–19 DS). Another case of dislocation of a myopic PRL into the vitreous cavity has been reported by the European Clinical Trial with PRL group (Philipson B. PRL (phakic posterior chamber IOL)—the 12 month results of the European clinical trial. Presented at the XXI Congress of the ESCRS-Munich 2003). I have recently reported a case of spontaneous dislocation of a PRL into the vitreous cavity in a young healthy female with high myopia 2 months postoperatively (spherical equivalent –19.5 D).6
The reported cases stress the importance of health and integrity of zonular apparatus in the long term stability of PCPIOLs. Since pseudoexfoliation is a progressive disease that may lead to progressive zonular disruption and spontaneous IOL-bag dislocation into the vitreous cavity even many years after cataract surgery,7 I think that PCPIOLs should not be used in pseudophakic eyes with pseudoexfoliation.