To analyze the effect of decentration on the optical quality of two diffractive-refractive intraocular lenses, a bifocal and a trifocal, when displaced laterally (horizontal direction) from the center.
The AT LISA 809M IOL (+3.75 D add) with two main foci and the AT LISA tri 839MP intraocular lens with three main foci (Carl Zeiss Meditec AG, Jena, Germany) were analyzed. The optical quality of the intraocular lenses was measured with the PMTF (power and modulation transfer function [MTF] measurement for refractive and diffractive intraocular lenses) optical bench (Lambda-X, Nivelles, Belgium). The optical quality of the lenses was evaluated by the MTF at different object vergences, the average modulation in the range of frequencies from 0 to 100 cycles/mm, and the through-focus MTF curves. All measures were recorded when the intraocular lenses were centered and decentered for 3.0- and 4.5-mm apertures. The Strehl ratio and the percentage of energy allocated at each focus at the centered position were also obtained.
Our results showed a lower optical quality with increasing decentration. The MTFs for the diffractive-refractive intraocular lenses decreased when the intraocular lenses were decentered. Also, the relative percentages of light energy allocated at each object vergence, for both intraocular lenses, agreed well with theoretical specifications and were consistent with the overall design of each lens.
The optical quality of these diffractive-refractive multifocal intraocular lenses was slightly reduced when the induced decentration was less than 0.4 mm. For a decentration of 0.4 mm, the maximum difference in average modulation values was about 18% compared to the centered position.