Compromise between spherical and chromatic aberration and depth of focus in aspheric intraocular lenses

PURPOSE: To evaluate the performance of 4 aspheric intraocular lenses (IOLs) in scotopic lighting conditions to determine the IOL with the best image quality at different spherical and chromatic aberrations and depths of focus. SETTING: Eye Institute, Optic Physiopathological Department, University of Florence, Florence, Italy. METHODS: Four IOLs were tested. In the Tecnis (Advanced Medical Optics, Inc.), IQ (Alcon Surgical), and KS-3Ai (Staar Surgical) IOLs, the aspheric profile is on the anterior surface of the optic. In the SofPort IOL (Bausch & Lomb), it is on the anterior and posterior surfaces and is preloaded in the injector. Spot diagrams were used to capture light dispersion, monochromatic point-spread function (PSF) to evaluate the light distribution on the fovea of the eye model, and monochromatic modulation transfer function (MTF) to evaluate image contrast. Depth of focus was evaluated at best focus and -0.08 mm and +0.08 mm from best focus. RESULTS: The spot diagrams for the Tecnis IOL were well-focused within a diameter of 10 mu m. For the other aspheric IOLs, the pattern was broader, indicating greater dispersion and larger chromatic aberrations. The monochromatic PSF and Strehl ratios favored the Tecnis lens, demonstrating that light energy is focused on the area of the eye model that represents the fovea. The monochromatic MTF showed higher contrast levels for the Tecnis lens than the other IOLs at yellow and blue wavelengths, but the KS-3Ai had higher contrast at the red frequency. The depth of focus testing showed overlapping of the yellow and blue frequencies and partial overlapping of the yellow, blue, and red for the Tecnis lens, indicating good depth of focus. The IQ IOL had higher luminance but less overlap. The SofPort and KS-3Ai IOLs had lower luminance thresholds. CONCLUSIONS: It is possible to find the compromise in which residuals of spherochromatic aberration enhance the depth of focus by decreasing the image sharpness or the amount of light on the fovea. The Tecnis IOL provided the best compromise between spherical and chromatic aberrations and depth of focus.