Evaluation of the longitudinal chromatic aberration generated by diffractive IOLs

Purpose:
To investigate some chromatic properties of hybrid refractive-diffractive extended depth of focus (EDOF) and multifocal IOLs using an optical bench and different illumination wavelengths.

Methods:
The induction and compensation of longitudinal chromatic aberration (LCA) were investigated on an optical bench using the through-focus energy efficiency (TFEE) curves of different wavelength for various hybrid refractive-diffractive EDOF, bi, and trifocal IOLs.
Results :
The LCA of each IOL can be estimated from the location of TFEE curves peaks for the tested wavelengths. For IOLs diffracting mainly in 0th and 1st order (green), the chromatic defocus is of refractive type for far foci (bi & trifocal), compensated for intermediate foci (trifocal), and reversed (diffraction dominant) for near foci (trifocal & bifocal). For IOLs diffracting in 1st and 2nd order (green), LCA is compensated for far and intermediate foci (EDOF and trifocal), and reversed for near foci (trifocal). However, there are important differences in height of energy peaks for blue and red wavelengths.
Conclusions:
It is theoretically possible to conceive diffractive lenses self-corrected for LCA at some of their foci. However, even when corrected for defocus, there are differences in the energy efficiency (peak height) obtained for the blue and red wavelengths.