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Abstract :
[en] Purpose:
To describe the optical performance of 3 types (monofocal, bifocal and trifocal) of diffractive hydrophobic intraocular lenses (IOLs).
Setting:
Fondation Rothschild, Paris, France
Methods:
An achromatic monofocal, a bifocal and trifocal diffractive IOLs were measured with an optical bench, designed to measure Modulation transfer function (MTF) and point spread function (PSF) of diffractive intraocular lenses. The measurements were performed at 3 wavelengths (480 nm, 546 nm and 650 nm), using an aberration free cornea and an aspherical artificial cornea generating a +0.28 µm of positive spherical aberration (ISO 11979-2 guideline). The through-focus MTF was recorded with the 3 IOLs for various pupil apertures. The evaluation of the magnitude of the halos was performed from PSF measurement obtained at each focal spot location.
Results:
The monofocal and the two bifocal IOLs were presenting 2 peaks on the through-focus MTF in the green: for intermediate vision (at 1.75D) for the monofocal achromatic lens, and for far and for near vision( at +4D) for the bifocal IOL of the same material. Three peaks were recorded with the trifocal IOL at any wavelength. The achromatic monofocal was monofocal for far in the red and monofocal for near in the blue. The amount of energy allocated to each focal point was not very different for the three IOLs except for smaller apertures where the distance vision with the trifocal IOL had a significant lower peak than the two other IOLs. The amount of halos were comparable between lenses.
Conclusions:
The diffractive and refractive optics generated opposite chromatic aberration. A achromatic diffractive IOL behaves like a bifocal IOL with an intermediate addition The bifocal and trifocal IOL induce similar chromatic effects for the near (bifocal, trifocal) and intermediate (trifocal) foci. The tested diffractive patterns wee not efficient to correct the chromatic aberration at the distance foci for all tested IOLs.
