Korean J Ophthalmol Vol.22, No.4, 2008 Table 2. Summary of results from analysis of the prediction error of refraction Procedures and data used Mean axial length Mean keratometric for calculation used* value used† Initial IOL implantation 23.54±0.61 44.40±1.67 Mean error of refraction† -0.13±0.67 Group In-the-bag IOL implantation group (n=9) In-the-sulcus Initial IOL implantation or optic capture IOL implantation group IOL exchange, (n=23) using secondary measurements IOL exchange, using secondary measurements IOL exchange, using initial measurements Significance (p-value)‡ IOL exchange, using initial measurements Significance (p-value)‡ 23.03±0.56 44.53±1.80 -1.10±1.15 23.54±0.61 0.440 23.82±0.80 23.45±0.88 23.82±0.80 0.464 44.40±1.67 0.008 44.13±1.44 44.22±1.42 44.13±1.44 <0.001 -0.26±0.87 0.021 0.47±0.70 -1.18±1.01 -0.55±0.92 0.004 Mean absolute error of refraction† 0.58±0.31 1.18±1.06 0.72±0.50 0.139 0.68±0.49 1.19±0.99 0.85±0.64 0.114 * units in millimeters; † units in diopters; ‡ Wilcoxon signed rank test: non-parametric. (p=0.464). D iscussio n There have been a number of clinical reports regarding the phenomenon of late postoperative opacification of hydrophilic acrylic IOLs.1-6,15-21 The involved IOLs included the Hydroview® (Bausch & Lomb) and the MemoryLens® (Mentor Ophthalmics, Inc.), which had calcified deposits mostly on the optic surface, and the Aqua-sense® (Ophthalmic Innovations International, Inc.), which had calcified deposits mostly within the IOL material. Furthermore, reports have been published in the Republic of Korea regarding late opacification of a hydrophilic acrylic IOL, the ACRL-C160® (Ophthalmed, USA).1-4 In such cases, an IOL exchange procedure may be the definitive treatment modality. However, there have been only a few reports regarding the surgical outcomes of IOL exchange.5,13,22,23 The principal purpose of this study was to review the clinical results, including the efficacy and complications, of IOL exchange due to an opacified IOL. Some authors4 have suggested that the pathogenic mechanism for late opacification of a hydrophilic acrylic IOL might be related to a systemic morbidity, such as diabetes mellitus. However, in our study, opacification of the IOL was readily observed in 37 eyes (71.2%) from non-diabetic subjects. In our study, the time interval between the initial cataract surgery and the IOL exchange was 60.4±7.4 months. A previous study1 reported that the development of hydrophilic acrylic IOL opacification was observed after 7.8±3.0 months in patients with diabetes mellitus and after 14.9±5.8 months 232 in those without diabetes. The large discrepancy between the previously reported time interval for initiation of IOL opacification and the time interval for IOL exchange surgery in our study can be explained by the fact that there may have been individual differences in the rate of progression of opacification and that some patients might have had useful vision despite opacification of their IOL. We believe that the decision to undergo a second surgery should be made deliberately and must take into account all potential risks and benefits. The intraoperative complication rates in our series were at least comparable to or relatively lower than those demonstrated by previous reports. Yu et al.5 reported 2 posterior capsule (PC) ruptures and 3 zonular dehiscences in a series of 15 explantation surgeries for calcified IOLs. Dagres et al.22 reported 1 case of PC rupture (4%), 10 cases of zonular dehiscence (40%), and 1 case with PC rupture and zonular dehiscence (4%) in 25 eyes. Gashau et al.13 reported a 23.1% occurrence rate of vitreous loss necessitating anterior vitrectomy. We observed zonular dehiscence in 4 eyes (7.7%) and iridodialysis in 1 eye (1.9%). Anterior vitrectomy was performed in 7 eyes (13.5%). The lack of vision-threatening complications in our study also demonstrates that the IOL exchange procedures were performed with sufficient safety. In our study, the mean BCVA after IOL exchange was 0.88±0.16 (0.07±0.15 logMAR) and the improvement in BCVA was statistically significant (p<0.001) with regard to the mean BCVA before IOL exchange, which was 0.48±0.16 (0.39±0.41 logMAR). Published reports on the mean BCVA before and after IOL exchange vary according to the surgeons. Dagres et al.22 reported a BCVA of 0.57±0.24