Optimal orientation for angularly segmented multifocal corrections

Abstract

Purpose: Evaluate the importance of orientation of multifocal lens designs with angular increments of addition.

Methods: Optical properties of one monofocal and three multifocal designs were analysed with the visual Strehl ratio (VSOTF) metric through-focus (-1 to 5 D). Designs were tested in combination with the higher-order aberrations (HOAs) of 782 subjects (1564 eyes). Simulations included one monofocal, one bifocal (eight orientations), one trifocal (four orientations), and a 4-foci design (four orientations). Monocular and binocular performances of all designs were assessed by computing the area under the through-focus VSOTF plots, the through-focus range of acceptable optical performance, and, for binocular combinations, optical disparity between left and right eyes.

Results: Under monocular conditions, bifocal designs generated larger areas under the through focus VSOTF than trifocal designs and 4-foci designs. Specifically, bifocal designs divided vertically were optimal for 48% of eyes. Trifocal designs and 4-foci designs offered longer intervals of acceptable through-focus vision. Coma and spherical aberration values were correlated with the optimal orientation of multifocal corrections. The best binocular combination was achieved with a monofocal and a trifocal lens. The orientation of a multifocal design with angular areas affected the final optical properties of the combination (lens plus eye).

Conclusions: The optical aberration distributions for our population of physiologically normal eyes demonstrated improved performance for some lens design orientations (i.e., left-right segments for 2-zone bifocals). Taking into account the HOAs of healthy patients, with special attention to coma and spherical aberration, will increase the optical quality of angularly divided multifocal solutions.

Keywords: angular segmentation; contact lenses; higher order aberrations; intraocular lenses; multifocal corrections; multifocality; optical quality; presbyopia; visual Strehl ratio.