Abstract
Purpose :
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. For many of the current presbyopia-correcting intraocular lenses the traditional methods for determining light distribution are not suitable, because of overlapping foci or even lack of discrete foci. The goal of this study was to develop a new method of determining the image (light) intensity produced by diffractive ophthalmic lenses over the visual defocus range from far to near.
Methods :
As in our previous study, 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. Care was taken that the incoming light intensity was kept at a constant level for all measurements. 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 (Airy disk for white light).
Design features measured included diffractive multifocal and extended depth of focus IOLs. An aspherical refractive monofocal lens which fully corrects the corneal monochromatic aberrations was used as a reference lens.
Results :
With the new method, 41 LSF images were recorded for each lens, over a defocus range from -4 to +1 diopter. Considering the linear relationship between the logarithm of the light intensity and visual acuity (Sheedy 1984), the measurement results are evaluated as log(intensity). The relative light intensity (RLI) is defined as log(intensity) of the study IOL divided by the log(intensity) of the monofocal reference IOL. For the distance focus, LRI is 0.93, 0.94 and 0.95 for the multifocal IOL, the extended depth of focus IOL, and the hybrid IOL, respectively.
At defocus levels exceeding -1 diopter, LRI was larger than 1.0 for all study lenses, which can be attributed to their presbyopia correcting nature, i.e. being multifocal or having an extended depth of focus.
Conclusions :
Measurements of through focus light intensity can be used to assess the light distribution and present the results in a clinically relevant metric, here called the relative light intensity (LRI).
This is a 2021 ARVO Annual Meeting abstract.