Long-term changes in intraocular lens position and corneal curvature after cataract surgery and their effect on refraction

PURPOSE: To evaluate the role of intraocular lens (IOL) position shift and changes in corneal curvature on long-term refractive shift after cataract surgery. SETTING: Rotterdam Ophthalmic Institute, Rotterdam, the Netherlands. DESIGN: Prospective cohort study. METHODS: Patients who had routine cataract surgery with implantation of a hydrophobic acrylic 1-piece IOL (Acrysof SA60AT) in the capsular bag were enrolled. Measurements were performed preoperatively and 1 month, 3 months, and 1 year postoperatively. Refraction was measured with the ARK-530A autorefractor. The IOL position and corneal curvature were measured with the Lenstar LS-900 biometer. The refractive effect of changes in IOL position and corneal curvature was calculated with a Gaussian optics-based thin-lens formula and correlated with the measured refractive shift. RESULTS: The study group comprised 59 eyes of 59 patients. The median measured absolute refractive change was 0.25 diopter (D). The IOL position showed a statistically significant mean posterior shift of 0.033 mm +/- 0.060 (SD) between 1 month and 1 year postoperatively (P < .01), of which the median calculated absolute refractive effect was 0.05 D. This did not correlate with the measured refractive shift (Pearson r = 0.10, P = .46). Natural fluctuations in corneal curvature caused a median calculated absolute refractive effect of 0.17 D, which correlated well with the measured refractive shift (Pearson r = .55, P < .001). CONCLUSIONS: Long-term changes in refraction after cataract surgery resulted from natural fluctuations in corneal curvature rather than from IOL position shift. These fluctuations limit the accuracy with which the refractive outcome can be planned.