Modulation transfer function in refractive‐diffractive multifocal intraocular lenses in vitro

Abstract

Abstract Purpose: The optical quality of two types of multifocal, hybrid refractive‐diffractive, intraocular lenses (IOL) is analyzed in vitro. Following the EN‐ISO international standard, the IOLs’ modulation transfer functions (MTF) are determined for both distance and near vision. The behaviour of these curves when the pupil size varies is studied. Methods: The IOLs analyzed were: AcrySoft ResTor SN60D3 (Alcon) and Tecnis ZM900 (AMO). The MTF was calculated from the cross line‐spread function recorded with the OPAL Vector System (Image Science Ltd. Oxford) by using fast Fourier transform techniques. The artificial eye model used simulates in vivo conditions of the anterior chamber including an artificial cornea and a physiological solution where the IOL were positioned. Following pupil sizes were analyzed: 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 mm. Results: The MTFs of the two multifocal IOLs analyzed show a good image quality for both in all conditions analyzed. However, a monofocal IOL with the same power (22.5 dioptres) provides a better image quality for distance vision. The Strehl ratio of the two multifocal IOLs decreases when pupil size increases, for both distance and near vision. To the contrary, the average modulation (from 0 to 100 c/mm) of the two multifocal IOLs remains approximately constant for all the pupil sizes. Conclusions: The image quality provided by the two multifocal refractive‐diffractive IOLs is very similar, although the quality with ResTor IOL is always slightly better than with Tecnis IOL in distance vision. In near vision, to the contrary. The conclusion is that when the distance vision improves the near vision worsens and vice‐versa.