Problems with diffractive IOLs
Authors: Grzybowski Andrzej 
Published: December 2022

In 2015, it was estimated that approximately 1.8 billion people were affected by presbyopia globally which was about 25% of the world population, and approximately 826 million people lacked proper visual correction. In the year 2030, the number of people with presbyopia is expected to be increasing to 2.1 billion people globally. two major IOL.

Treatment and correction of presbyopia have become challenging with increasing demands and expectations of patients since there are no drugs or procedures that can cause perfect vision at all distances without risk. Surgical options, corneal or intraocular, are of increasing interest since they are based on most modern technologies. There are still risks of surgical complications, which are hardly reversible, and the best results are based on careful selection of patients. Moreover, good understanding of the limitation of the present technologies by patients and their trade‐off nature are very important, for example, patients who gain spectacle‐free of near or intermediate vision may experience some dysphotopsias in different lighting conditions or lose some sharpness of vision or stereopsis depending on the offered technology. Multifocal IOLs (MIOLs) can be made using refractive and diffractive surfaces or combination of both. The optical power in the refractive design decreases continuously from the center to the periphery of the lens creating an infinite number of focal points and is derived from the smooth hyperbolic shape of its optics. Thus, the performance of refractive design IOLs is dependent on pupil size and IOL centration. On the other hand, a diffractive IOL generates multifocality making use of light interference and is independent of pupil size. It incorporates a pattern consisting of a series of annular concentric grooves less than one micron in depth, which are engraved around the optical axis on either the front or the back surface of a lens (the echelette technology). One of the recent studies from Japan reported that patients implanted with diffractive multifocal IOLs had notable declines in the corrected distance visual acuity, distance corrected near VA, and near area of focus with aging.

When compared to monofocal IOLs, MIOLs will always be related with poorer quality of vision. Moreover, good understanding of the limitation of the present technologies by patients and their trade‐off nature are very important, for example, patients who gain spectacle‐free of near or intermediate vision may experience some dysphotopsias in different lighting conditions or lose some sharpness of vision or stereopsis depending on the offered technology. Halos, glare, reduced contrast sensitivity or reduced retinal illumination are relatively common problems with MIOLs. Halos depend on the intensity and size of the out‐of‐focus image corresponding to the other foci produced by the lens, that is secondary to add power and energy distribution among foci. Moreover, if aberrations are used in their design, their position and centering might be crucial. MIOLs do not replicate the natural condition, thus patients with MIOLs must learn and adapt to their use with so called binocular neuro‐adaptation.