Peripheral defocus of monofocal intraocular lenses

Abstract

Purpose: To quantify the angular-dependence of monofocal intraocular lens (IOL) power. Setting: Ophthalmic Biophysics Laboratory, Kallam Anji Reddy campus, L V Prasad Eye Institute, Hyderabad, India. Design: Laboratory study. Methods: Experiments were performed on IOLs from two different manufacturers (APPALENS 207, Appasamy Associates and SN60WF, Alcon Laboratories). IOL powers ranged from 17 to 25 D. The IOLs were mounted in a fluid-filled chamber and the on-axis and off-axis powers were measured using a laser ray tracing system over the central 3 mm zone with delivery angles ranging from -30° to +30° in 5° increments. The position of the best focus was calculated for each IOL at each angle. The angular dependence of IOL power was compared with theoretical predictions. Results: Peripheral defocus increased significantly with increasing incidence angle and power. The peripheral defocus at ±30° increased from 5.8 D to 8.5 D when the power increased from 17.5 D to 24.5 D for APPALENS 207 and from 4.9 D to 7.4 D when the power increased from 17 D to 25 D for SN60WF. The mean difference between the measured and theoretical tangential power at ±30° was 0.50 ± 0.16 D for the APPALENS 207 and -0.40 ± 0.10 D for the SN60WF, independent of IOL power. Conclusions: IOLs introduce a significant amount of peripheral defocus which varies significantly with IOL power and design. Given that peripheral defocus is related to lens power, replacement of the natural lens (approximately 24 D) with an IOL will produce a significant difference in peripheral defocus profile after surgery.