Korean J Ophthalmol Vol.22, No.4, 2008 and SPSS (version 12.0, SPSS Inc, Chicago, IL). Results were considered statistically significant only when the p-value was less than 0.05. Results Table 1 presents a summary of the total cases. The subjects included were 36 men (75%) and 12 women (25%); the mean age of the patients was 70.1±7.8 years (range: 49-84). Four of the male patients had undergone bilateral IOL exchanges. Fourteen patients (29.2%) were diabetic and 23 patients (47.9%) had systemic hypertension. Fifteen eyes (31.3%) were from diabetic patients, of which 10 (19.2%) had no diabetic retinopathy, 2 (3.9%) had mild nonproliferative diabetic retinopathy, and 3 (5.8%) had moderate nonproliferative diabetic retinopathy according to the early treatment of diabetic retinopathy study (ETDRS) criteria.14 Other ocular comorbidities included glaucoma in 4 eyes (7.7%), a preexisting superotemporal branch retinal vein occlusion in 1 eye (1.9%), and a magnetic resonance imaging-proven orbital mass encircling the optic nerve in 1 eye (1.9%). The initial procedure was a phacoemulsification surgery in 49 eyes and an extracapsular cataract extraction in 3 eyes. The mean time interval between initial IOL implantation and the IOL exchange was 60.4±7.4 months (range: 49.0-81.3) and the mean length of follow-up after IOL exchange was 15.6±11.4 months (range: 1.5-38.5). During IOL exchange, a new IOL was implanted in the bag in 13 eyes (25.0%) and in the sulcus in 39 eyes (75.0%) with or without optic capture. Zonular dehiscence occurred in 4 eyes (7.7%) and iridodialysis in 1 eye (1.9%). Preexisting posterior capsular incompetency was observed in 4 eyes (7.7%). Seven eyes (13.5%) were treated with concomitant anterior vitrectomy. During postoperative follow-up, 8 eyes (15.4%) were treated with a Nd:YAG posterior capsulotomy because of posterior capsular opacification. One eye (case 19) that had developed a delayed IOL dislocation associated with severe capsular contracture was treated with IOL repositioning by suture fixation to the sclera. Aside from case 19, no eye developed serious complications such as endophthalmitis, intractable corneal decompensation, or retinal detachment. IOP elevation was observed in 13 eyes (25%) after 1 week, in 5 eyes (9.6%) after 1 month, and was normalized in all cases at the last outpatient visit. The best recorded BCVA after initial IOL implantation was available in 51 cases (case 38 was the exception). The mean BCVA was 0.90±0.16 (0.06±0.15 logMAR) after initial IOL implantation, 0.48±0.16 (0.39±0.41 logMAR) before IOL exchange, and 0.88±0.16 (0.07±0.15 logMAR) after IOL exchange. A paired t-test revealed that the mean BCVA before IOL exchange improved significantly after IOL exchange (p<0.001) and it was not significantly different from the mean BCVA obtained after the initial IOL 230 implantation (p=0.130). There was an increase of nearly 4 lines in the mean BCVA after IOL exchange. Table 2 summarizes the results of the analysis on the prediction error of postoperative refraction for the IOL exchange. In 32 eyes (cases marked with an asterisk (*)), the keratometric value and the AL were determined both before the initial IOL implantation and before the IOL exchange. The mean keratometric values before initial IOL implantation and before IOL exchange were 44.20±1.48 diopters (D) and 44.30±1.51 D, respectively, while the mean ALs were 23.74±0.75 mm and 23.30±0.82 mm, respectively. A paired t-test revealed that the difference between ALs was statistically significant (p<0.001), while the difference in the mean keratometric values was not significant (p=0.222). A mean shortening of the ALs of about 0.43 mm was observed before the IOL exchange. In the group with new IOL implantation in the bag (9 cases), the mean prediction error and the mean absolute error for the initial IOL implantation were -0.04±0.66 D and 0.56±0.30 D, respectively. The mean prediction error and the mean absolute error for the IOL exchange calculated from the measurement data taken before the IOL exchange were -1.10±1.15 D and 1.18±1.06 D, respectively. The mean prediction error and the mean absolute error for the IOL exchange using the data taken before the initial IOL implantation were -0.26±0.87 and 0.72±0.50 D, respectively. The two biometric data resulted in significantly different mean prediction errors (p=0.021), indicating significantly better refractive prediction with biometric data obtained before the initial IOL implantation. The mean ALs before the initial IOL implantation and before the IOL exchange were 23.54±0.61 mm and 23.03±0.56 mm, respectively. The mean keratometric values before the initial IOL implantation and before the IOL exchange were 44.40±1.67 D and 44.53±1.80 D, respectively. A Wilcoxon signed rank test showed that the difference in mean AL measurements was statistically significant (p=0.008), while the difference in mean keratometric values was not significant (p=0.440). For the in-the-sulcus group (23 cases), the mean error and the mean absolute error were 0.49±0.72 D and 0.70±0.50 D for the initial IOL implantation, -1.18±1.01 D and 1.19±0.99 D for the IOL exchange using the data taken before the IOL exchange, and -0.55±0.92 D and 0.85±0.64 D for the IOL exchange using the data taken before the initial IOL implantation, respectively. These two biometric data resulted in a significantly different mean prediction error for the IOL exchange (p=0.004). A better refractive prediction was associated with the biometric data obtained before the initial IOL implantation. The mean ALs measured before the initial IOL implantation and before the IOL exchange were 23.82±0.80 mm and 23.45±0.88 mm, respectively, while the mean keratometric values were 44.13±1.44 D and 44.22±1.42 D, respectively. A Wilcoxon signed rank test showed that the difference in mean AL was significant (p<0.001). In contrast, the difference in mean keratometric values was insignificant