patients who have already undergone a monofocal IOL implantation surgery may also be benefited from an IOL exchange procedure. The principal purpose of this study is to evaluate the clinical outcome of IOL exchange, including its efficacy in visual recovery and its complications. This study also provides some insight into the determination of adequate IOL power for IOL exchange performed for the eyes with an opacified IOL. M aterials and M etho ds The present study includes consecutive cases of 52 eyes from 48 patients treated with IOL exchange at the Korean Veterans hospital between January 2005 and December 2006. Before the IOL exchange surgery, IOL power was calculated using the keratometric value and the axial length (AL) obtained either before the initial cataract surgery or before the IOL exchange. In 32 cases, reevaluation of biometric values was performed using an autokeratore- fractometer (Humphrey-Zeiss model 599, USA) and an applanation ultrasound (US) A-scanner (Paradigm Medical Industries model p37, USA) using the mean pseudophakic US velocity of 1533 m/sec in pseudophakic mode. All of the IOL measurements for initial IOL implantation taken in our hospital were performed by one technician and all of the repeat IOL measurements before the IOL exchange were done by another technician. The SRK/T formula was used to calculate IOL power. All IOL exchange surgeries were performed by one experienced surgeon. Retrobulbar anesthesia using 2% lidocaine was used in all cases. After a 1.2 mm-sized clear corneal paracentesis incision was made at the temporal side, a superior scleral tunnel incision was made with a width of approximately 6 mm. The ophthalmic viscoelastic device was then introduced into the anterior chamber. A 23 gauge needle with a bent tip was used to relieve adhesion between the lens capsule and the opacified IOL. Usually there were firm adhesions between the lens capsule and the IOL, and care was taken not to exert excessive force. Viscodissection was carefully applied to further relieve the adhesions and to safely separate the IOL haptics from the lens capsule. In some cases in which there were excessively strong adhesions, one or both of the haptics had to be cut with Vannas scissors and left in the capsular bag to avoid damage to the lens capsules and/or the zonules.5,13 The optic was also sometimes bisected before removal. After safely removing the opacified IOL, a new foldable posterior chamber IOL was inserted either into the capsular bag or into the ciliary sulcus. In all cases in which the size of the capsulorhexis opening was smaller than the optic size, optic capture with the anterior capsule was attempted. Two types of IOLs were used for the exchange procedures: Sensar® (Advanced Medical Optics, USA) and Acrysof® (MA60BM)(Alcon, USA). Finally, the viscoelastic device was removed by irrigation and aspiration and the SM Kim, et al. INTRAOCULAR LENS EXCHANGE scleral wound was closed with interrupted 10-0 nylon sutures. During postoperative follow-up, visual acuity (VA), refraction, and intraocular pressure (IOP) were monitored. VAs were evaluated with a standard Snellen chart and converted to logMAR for statistical analysis. VA that could barely detect a hand movement was defined as 0.001 in decimal scale. Refractions were measured by an autokeratorefractometer (Humphrey-Zeiss model 599, USA), confirmed by subjective refractions, and converted to spherical equivalents (SEs) for statistical analysis. Postoperative best corrected visual acuity (BCVA) and refraction were obtained at least 1 month after each operation. The IOP was considered to be elevated when it exceeded 21 mmHg or was increased by more than 5 mmHg with regard to its preoperative level. Data collected included age, gender, presence of systemic (diabetes mellitus and hypertension) and/or ophthalmic comorbidities, interval between initial IOL implantation and IOL exchange, site of IOL implantation during the IOL exchange, intraoperative complications and execution of anterior vitrectomy during the IOL exchange procedure, length of postoperative follow-up after the IOL exchange, pre- and post-exchange VAs and IOPs, and execution of an Nd:YAG posterior capsulotomy after the IOL exchange. The following data were also retrieved when available: Type of initial cataract surgery, power and material of the initially implanted IOL, site of IOL implantation, biometric data used for the IOL calculation (both for the initial and the exchange procedures), IOL calculation formula, and the BCVA and refractions after the initial IOL implantation. We analyzed the complications related to the IOL exchange and their incidences. The mean BCVA obtained after IOL exchange was compared with that recorded before IOL exchange and, when available, also with the mean BCVA obtained after the initial IOL implantation surgery. For 32 cases in which the biometric data obtained both before the initial IOL implantation surgery and before the IOL exchange were available, further analysis was conducted regarding the predictability of postoperative refraction. The prediction error of postoperative refraction was defined as the actual obtained postoperative SE minus the intended SE given the implanted IOL power, and its absolute value was defined as the absolute error. Cases included in this analysis were grouped according to the site of IOL implantation during IOL exchange; there was an in-the-bag implantation group and an in-the-sulcus group. The refractive results were compared between these two groups. Within each group, the prediction error for the IOL exchange was then compared with the prediction error for the initial IOL implantation surgery. The reevaluated keratometric value and AL were also compared with the values obtained before the initial IOL implantation surgery. The prediction errors of refraction which were calculated using these two biometric datasets were compared. Statistical analyses were performed using Microsoft Excel 229