Factors leading to lens implant decentration and exchange

Purpose To examine the intra- and postoperative factors leading to posterio r chamber intraocular lens (IOL) decentration in patients requiring IOL exc hange, and to identify avoidable causes of IOL decentration. Methods Case records of 17 patients who had undergone posterior chamber IOL exchange were examined for: (i) any complication or alteration to the orig inal intended surgical procedure, (ii) IOL type and position at the complet ion of initial surgery, (iii) IOL position at the time of re-operation. Results The decentred lens implants were injected silicone plate-haptic IOL s in 10 patients, small (5.5 mm) optic diameter PMMA IOLs in 4 patients and large (7 mm) optic diameter PMMA IOLs in 3 patients. In all cases, decentr ation was due to IOL subluxation. Early decentration of the injected lenses was due to IOL implantation in eyes without a continuous capsulorrhexis. I n contrast late decentration was due to subluxation associated with capsule fibrosis. Decentration of small optic FMMA IOLs was found to be associated with an anterior capsule tear and haptic malposition in the ciliary sulcus . Decentration of large optic PMMA IOLs was associated with posterior displ acement of one haptic through a posterior capsule defect, zonule dehiscence or fixation of one haptic in the sulcus and one in the capsule bag. Conclusion Clinically significant postoperative subluxation of injected sil icone IOLs may be minimised by implanting only into a lens capsule bag with an intact capsulorrhexis. The risk of decentration of small optic PMMA IOL s may be minimised by positioning the haptics at 90 degrees to any capsulor rhexis tear. After cataract surgery complicated by posterior capsule ruptur e or zonule dehiscence, it is important to assess the remaining capsule sup port and, where sufficient, implant a large optic diameter posterior chambe r IOL in the ciliary sulcus.