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RESEARCH PRODUCT

Evaluation of the performance of multifocal intraocular lenses image quality: analysis of the standard methods

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Purpose: To analyze the standard methods used to describe intraocular lenses (IOL) and to suggest some improvements to make them applicable for multifocal IOLs. Methods: The EN-ISO standards and the standards of the American National Standards Institute (ANSI) for the evaluation of the performance of IOLs are tested for multifocal IOLs. The MTF of the one refractive multifocal IOL and two hybrid refractive-diffractive multifocal IOLs is measured for both distance focus and near focus and using different pupil sizes. Results: The average modulation (AM) from 0 to 100 c/mm of multifocal IOLs (for the distance focus) is about 40-50% lower than the AM of monofocal IOLs, for all pupil sizes studied. This fact suggests that the EN ISO standards must be revised in some points to be adapted for multifocal IOLs. Moreover, the near focus of the refractive IOL only appears beyond 3.5 mm of pupil size; in consequence this type of multifocal IOL could not be described only with a 3 mm pupil as stated in ISO standard. The width at half height of the point spread function (PSF) or the cut-off frequency value of the MTF, are not useful for multifocal IOLs. Multifocal IOLs can have a narrow PSF at half height but be very wide at the bottom, occuring this even in some so-called apodized IOLs. The cut-off frequency value is also useful in monofocal lenses as quality factor to compare MTFs of different lenses or pupil sizes because an approximately uniform slope for the MTF is suppose. Conclusions: EN-ISO and ANSI, demand the modulation of only one pupil and one frequency: 3 mm and 100 c/mm. We recommend to measure at least with 2 different pupils and to give the AM value for both distance and near focus.