Optical performance of a new design of a trifocal intraocular lens based on the Devil's diffractive lens

Abstract

In this work, we propose a new diffractive trifocal intraocular lens design with focus extension, conceived to provide a high visual performance at intermediate distances. This design is based on a fractal structure known as the "Devil's staircase". To assess its optical performance, numerical simulations have been performed with a ray tracing program using the Liou-Brennan model eye under polychromatic illumination. The simulated through the focus visual acuity was the merit function employed to test its pupil-dependence and its behavior against decentering. A qualitative assessment of the multifocal intraocular lens (MIOL) was also performed experimentally with an adaptive optics visual simulator. The experimental results confirm our numerical predictions. We found that our MIOL design has a trifocal profile, which is very robust to decentration and has low degree of pupil dependence. It performs better at intermediate distances than at near distances and, for a pupil diameter of 3 mm, it works like an EDoF lens over almost the entire defocus range.

Fig. 1.

a) Triadic Cantor fractal set developed up to S = 3. The structure for S = 0 is the initiator and the one corresponding to S = 1 is the generator constructed by dividing the initiator into equal parts of length 1/3 and removing the central one. This procedure is continued at the subsequent stages S = 2 and S = 3. b) Cantor function or Devil’s staircase, $F_3(x)$ derived from the triadic Cantor fractal set represented in a).

Fig. 2.

Diffractive profile of a Devil’s MIOL with an addition of 3.5 D. The green and red lines represent pupil radius 3 mm and 4.5 mm, respectively. Dotted vertical lines mark the steps of the Devil’s staircase.

Fig. 3.

MTFa curves for 3.0 mm and 4.5 mm pupils obtained for wavelengths 450 nm (blue line), 550 nm (green line), 650 nm (red line), and polychromatic light (black line) for the Devil’s MIOL and monofocal IOL (dotted black line).

Fig. 4.

MTFa values for the distance, intermediate and near foci obtained for pupils varying from 3.0 mm to 4.5 mm.

Fig. 5.

a) VA defocus curves with the Devil’s MIOL, obtained from polychromatic MTFa values using Eq. (4). The solid black line shows the VA with the lens centered. The dashed magenta line was obtained with the MIOL temporally off-centered 0.25 mm, b) Simulated images obtained (from the PSFs) of an optotype with letters whose sizes correspond to visual acuities of 0.0 logMAR, 0.2 logMAR, and 0.4 logMAR. These images were calculated at the main foci of the MIOL for the centered (black box) and decentered (magenta box) lens. c) The same as in b), but computed for a monofocal IOL

Fig. 6.

Images of a tumbling E optotype corresponding to 0.4, 0.2, and 0.0 logMAR VA obtained with the VAO system simulating the Devil’s MIOL.