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Letter

Spherical and chromatic aberration in aspherical IOLs

Preussner, Paul-Rolf MD, PhD

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Journal of Cataract & Refractive Surgery: October 2007 - Volume 33 - Issue 10 - p 1676
doi: 10.1016/j.jcrs.2007.04.046
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In a recent article, Franchini1 reports his investigations of 4 intraocular lens (IOL) models. I tried to follow his calculations with my own software and my own data but found the following inconsistencies:

Other than stated in the article, the IOLs shown in Figure 2 do not have the same power of 20.0 diopters (D) as claimed by the author. With the data for vertex radii and central thickness, the Tecnis (n = 1.46) has 19.0 D, the SN60WF (n = 1.554) has 19.5 D, and the SofPort (n = 1.427) has 22.0 D. These powers result from the paraxial thick lens definition as required in ISO11979-2. (I could not calculate the power for the AQ-310ai because I do not know the refractive index.)

For the description of aspherical surfaces, parameters such as numerical eccentricity (e), asphericity Q = −e2, and conic constant c = Q + 1 are common. The convention adopted by the author's “k” does not fit any of these definitions; moreover, it is not steady following the examples for sphere, parabola, ellipsis, and hyperbola given in the text. For principal mathematical reasons, steadiness is required; ie, the value for a circle should be between the values for oblate and prolate ellipsis.

The same measure (k) given in Figure 2 is not consistent with the manufacturer's data, at least for the Tecnis and for SofPort IOLs. So, unfortunately, I had to stop my attempt to follow the author's calculations.

REFERENCE

1. Franchini A. Compromise between spherical and chromatic aberration and depth of focus in aspheric intraocular lenses. J Cataract Refract Surg. 2007;33:497-509.
© 2007 by Lippincott Williams & Wilkins, Inc.