LCA discussion on diffractive intraocular lenses: a new optical design to correct chromatic aberration

Methods:
The effects of Abbe number and the topography of different diffractive IOL profiles were evaluated. On the basis of MTF through-focus curves at different light wavelengths (red, blue and green) and for different pupil apertures, polychromatic behavior of various diffractive multifocal IOLs was assessed. Pin-hole effect will also be discussed and addressed with the point of view of chromatic effect.
Results:
Diffractive multifocal IOLs show chromatic aberration especially along the axis (LCA-longitudinal Chromatic aberration) but also out of the optical axis. These chromatic aberrations are the results of the refractive chromatic properties of the lens, driven by the biomaterial refractive indexes and the IOL diffractive pattern. Refractive effects are mainly controlled by the biomaterial Abbe number while diffractive effects are controlled by the topography of the diffractive pattern.
Conclusions:
Refractive effects are mainly controlled by biomaterial Abbe number while diffractive effects are controlled by diffractive pattern topography. The insertion of a multifocal diffractive lens following crystalline lens extraction may significantly modify the chromatic aberration of the pseudophakic eye. Chromatic aberrations induce vision losses due to sharpness reduction of (any) object edges. The contrast sensitivity as well as the visual acuity are then reduced. This fact has especially been proven with measurements on optical benches. Moreover, diffractive and refractive effects act in an opposite ways and can in principle be compensated. However rules to creates an achromatic lens based on refractive-diffractive principles are quite complex.