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Gatinel D, Azar DT, Dumas L, Malet J. Effect of Anterior Corneal Surface Asphericity change we Fourth - Order Zernike Spherical Aberrations. J Refract Surg. 2014; 30 (10): 708-715

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This article is devoted to the study of the relationship between changes in the Asphericity and those of the spherical aberration of corneal origin. In refractive surgery presbyopia, much multifocal corrections in LASIK (presbyLASIK) is based on the correction of a defocus (D) possible, and a modulation of the Asphericity corneal (Q) to induce a corneal multifocalite causing a myopisation Central and peripheral emmetropisation. Is this differential of refraction at spherical aberration (Z40) negative.

The goal of multifocal correction is to vary the ΔZ40 spherical aberration to a more negative value. For a correction of myopic (or hypermetropique) D and a modulation desired of asphericity (ΔZ40), what is the value of Q to aim to get this fix and you want change? A mathematical model has been built to meet this apparent; the front of the cornea is modeled as an aspherical surface profile is described by a conic section. The issuance of a profile of aspheric ablation allows to correct the paraxial (D) defocus and modulate the corneal Asphericity (Q). We have calculated for various corrections of defocus (myopia and hyperopia), what was the variation of asphericity to program to get a variation of the desired spherical aberration (ex: ΔZ40 = - 0.4 microns on a 6 mm optical zone). The main result of this study concerns the fact that for the correction of hyperopia, the variation of asphericity (ΔQ) to obtain a variation of spherical aberration (ΔZ40) of the order of-0.4 microns is relatively constant and close to ΔQ = - 0.6. This suggests the possibility of establishing a nomogram simplified for the correction of presbyopia and hyperopia.

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