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Reply: Limited accuracy of Hartmann-Shack wavefront sensing in eyes with diffractive multifocal IOLs

Toto, Lisa MD; Falconio, Gennaro MD; Vecchiarino, Luca MD; Scorcia, Vincenzo MD; Di Nicola, Marta PhD; Ballone, Enzo PhD; Mastropasqua, Leonardo MD

Journal of Cataract & Refractive Surgery: April 2008 - Volume 34 - Issue 4 - p 528-529
doi: 10.1016/j.jcrs.2007.11.050
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We agree with Gatinel that in general, there is a lack of information on the Shack-Hartman wavefront sensors on the higher-order aberrations and scattering related to the limitation imposed by the small lens sampling. However, the H-S wavefront sensor used in our study was a Wasca wavefront analyzer aberrometer (Asclepion-Meditec AG) with 1452 lenslets for 9.0 mm of analysis—the highest number of lenslets among the commercially available ocular wavefront sensors. A precise definition and calculation of aberrations in terms of Zernike polynomials up to the 4th order is therefore possible.

Gatinel is right in pointing out that the wavefront error induced by DMIOLs could be underestimated or wrongly reconstructed by the H-S device because of mismatches between concentric diffractive steps and square microlens array. However, our results confirm that the Tecnis ZM900 multifocal IOL, which was created to induce low spherical aberrations, similar to monofocal aspherical IOLs, is related to a lower spherical wavefront error compared with the AcrySof ReSTOR multifocal IOL, thus demonstrating a reliable analysis of symmetrical aberrations such as spherical aberration.

Gatinel added that the H-S wavefront sensor provides no information about scattering that contributes, together with diffraction and aberrations, to a degradation of retinal image quality. Scattering that is normally small after cataract extraction and implantation of conventional IOLs increases after DMIOL implantation.

We agree that double-pass techniques, which are also sensitive to scattering, would permit a more precise objective evaluation of the optical quality of eyes with DMIOLs. At the same time, we think a subjective evaluation of visual performance such as measurement of contrast sensitivity or visual acuity at low contrast, as performed in our study, is productive and provides indirect information about the total optical degradation of the eye.

© 2008 by Lippincott Williams & Wilkins, Inc.