OBJECTIVE To assess the long-term clinical outcomes of implantation of a lens consisting of a biocompatible collagen copolymer (Visian implantable Collamer lens [ICL]; STAAR Surgical, Nidau, Switzerland) for moderate to high myopia. METHODS We evaluated 56 eyes of 34 patients with myopic refractive errors of -4.00 to -15.25 diopters (D) who underwent ICL implantation and routine postoperative examinations. Before and 1, 3, and 6 months and 1, 2, and 4 years after surgery, we assessed the safety, efficacy, predictability, stability, and adverse events of the surgery. RESULTS Mean (SD) logMAR uncorrected and best spectacle-corrected visual acuities were -0.03 (0.23) and -0.21 (0.09), respectively, at 4 years after surgery. The mean (SD) safety and efficacy indexes were 1.19 (0.25) and 0.83 (0.29), respectively. At 4 years, 44 (79%) and 52 (93%) of the eyes were within +/-0.5 and +/-1.0 D, respectively, of the targeted correction. Mean (SD) manifest refraction changes of -0.24 (0.57) D occurred from 1 month to 4 years after surgery. No vision-threatening complications occurred during the observation period. CONCLUSIONS Implantation of ICLs is safe and effective and provides predictable and stable refractive results in the treatment of moderate to high myopia during a 4-year observation period, suggesting its viability as a surgical option for the treatment of such eyes.