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Proceedings Paper

Ergonomic criterion for lens quality
Author(s): Eliezer Keren; Eli Bar-Ami; Franck Nabeth; Shmuel Yaacov
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Paper Abstract

The traditional parameters used for describing lens performance, such as PSF of MTF, fail to take into account the contribution of the human visual system to image quality. The proposed criterion assumes that the eye responds through accommodation and achieves a 'best focus' situation. The best focus is defined as that focal length where the maximal amount of radiation falls within a certain depth-of-focus interval. The depth range is determined by the eye's ability to detect power changes, which is around 0.25 diopters. The distribution of focal power over the lens aperture is measured with a moire deflectometer. Convolving the distribution with a smearing function of width equal to the dioptic depth parameter produces a power profile as perceived by the visual system. The maximum of this seared distribution defines the measured power of the lens, and the value of the distribution at the maximum, normalized by the total area under the curve, is the quality figure of the lens. The new parameter, giving the encircled energy with the focal depth range, may be refined by taking into account other features of lens fabrication and human response. In particular, the distribution is weighted according to the radial distance from the lens center. With high- power lenses with their inherent spherical aberration, less weight is given to more distant portions of the lens. The measurement of lens quality is demonstrated with a large number of soft contact lenses measured in solution. These lenses exhibit a wide range of distortions and imperfections.

Paper Details

Date Published: 26 May 1994
PDF: 8 pages
Proc. SPIE 2127, Ophthalmic Lens Design and Fabrication II, (26 May 1994); doi: 10.1117/12.176833
Show Author Affiliations
Eliezer Keren, Rotlex Optics Ltd. (Israel)
Eli Bar-Ami, Hanita Lenses (Israel)
Franck Nabeth, Rotlex Optics Ltd. (Israel)
Shmuel Yaacov, Rotlex Optics Ltd. (Israel)


Published in SPIE Proceedings Vol. 2127:
Ophthalmic Lens Design and Fabrication II
Donn Michael Silberman, Editor(s)

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