Abstract
Purpose :
Multifocal lenses in presbyopia correction suffer from degraded intermediate distance image quality. The performance of the lenses can also be pupil-size dependent. The goal of this study was to evaluate a new approach to designing refractive presbyopia-correcting ophthalmic lenses.
Methods :
Theoretical simulations were conducted. The regional optical power (φ) of the lens cycles continuously between far and near across the pupil radius, r. In each cycle, the power is represented by the formula φ(r)= A(r)×tri((2rM/R)N)×P, where P is the dioptric power range, N is the exponent inside the triangular function(tri). M determines the number of cycles within a pupil with radius R, and A(r) is a pupil apodization function. The power profile is subsequently converted into a wavefront and then into the point spread function (PSF). Through-focus retinal image quality is evaluated using a 20/20 Snellen letter ‘E’ convolved with the polychromatic PSF. A visual quality metric, area under modulation transfer function (areaMTF), is calculated for three defocus ranges: far (0-0.83 diopters(D)), intermediate (0.83-1.67D), and near (1.67-2.5D). A global search was programed to test the through-focus visual quality under different combinations of the aforementioned parameters.
Results :
A design example for a 6mm pupil was found by the global search and used to evaluate the performance through focus. The average areaMTF for the far, intermediate, and near ranges was well balanced for a relatively large pupil (4 and 5mm) while the far was slightly degraded for a 3mm pupil. Further refinements could be made by applying an apodization A(r), which served to redistribute relative light energy to the three ranges. Although the image quality at far was compromised compared to a monofocal design, the orientation of the convolved 20/20 letter ‘E’ was clearly recognized subjectively over the whole defocus range from 0 to 2.5D.
Conclusions :
The designing method based on continuous periodic power profile was introduced and tested theoretically. This approach can yield a design for a presbyopia-correcting ophthalmic lens with excellent retinal image quality through a focus range of at least 2.5D and is independent of pupil size changes. Although visual performance with this design needs to be tested in the future, this new design approach could overcome the current limitations of multifocal lenses for presbyopia correction.
This is a 2020 ARVO Annual Meeting abstract.