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Henk A Weeber, Robert Rosen, Franck Gounou, Patricia Piers; Light intensity distribution of diffractive ophthalmic lenses. Invest. Ophthalmol. Vis. Sci. 2020;61(7):580.
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© ARVO (1962-2015); The Authors (2016-present)
The diffractive efficiency is traditionally defined as the ratio of usable energy relative to total incident energy for individual diffraction orders of a diffractive optical element. This becomes complicated for diffractive ophthalmic lenses, especially those providing extended depth of focus since they produce a continuous range of vision rather than discrete foci. The goal of this study was to assess the image (light) intensity produced by diffractive ophthalmic lenses at different defocus ranges, compared to a standard monofocal lens.
Light intensities were measured in an optical setup consisting of a white light source, slit target, collimator, cornea, liquid cell, relay lens and imaging camera. The image (line spread function, LSF) was recorded over a range of defocus positions. Light intensity was evaluated over the central part of the LSF up to the first minimum of the image of a diffraction limited system. This size of the Airy disk corresponded to 19 pixels. Design features measured included multifocal, extended depth of focus, and different chromatic aberration features. An aspherical refractive monofocal lens was used as the reference lens. All lenses had the same spherical aberration correction. Relative light intensity was calculated compared to the reference lens and quantified in linear and logarithmic scales.
For the distance image, the light intensity of the diffractive lenses was between 50-60% of that of a monofocal lens, corresponding to 50% for multifocal lenses and between 54-60% for extended depth of focus lenses with partial correction of chromatic aberration. The average light intensity over the defocus range from distance to near of the diffractive lenses was the same or very similar to that of the monofocal reference lens, and was highest for those lenses having an extended depth of focus feature and partial correction of chromatic aberration.
Measurements of through focus light intensity provides a useful method to characterize diffractive ophthalmic lenses. Considering the functional defocus range of diffractive ophthalmic lenses, the average light intensity of the diffractive ophthalmic lenses was found to be the same or similar to that of refractive lenses. While diffractive lenses are often thought of having distinct foci, the light intensity of some diffractive lenses show little variation over a range of defocus values.
This is a 2020 ARVO Annual Meeting abstract.
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