Impact of zone geometry on the introduction of myopic defocus in young eyes wearing multizone lenses.

Abstract

Purpose : Multizone soft contact lenses (SCL) have been shown effective to control myopia progression in young eyes due to proposed introduction of myopic defocus. This project investigated the myopic defocus introduced and how this varied as a function of lens geometry.

Methods : Ten healthy young adult, myopic subjects were binocularly fitted with each of 4 contact lenses in a random order. Lenses included single vision (SV), concentric-ring dual-focus (DF), center-distance multifocal (MF), and a new multi-zone optical design with RingBoost^TM (RB) technology. A Shack-Hartmann aberrometer was modified to allow open field binocular viewing and capture full natural pupil wavefront aberrations of right eyes at 4 target vergences (TVs) between -0.25 and -4.00 D. Wavefront data were processed using a custom MATLAB program. Eye plus lens defocus was quantified as the difference between the measured refractive state (RS) and target vergence (TV) based on the average of all lenslet samples within each zone of the multizone designs throughout the entire pupil and compared to equivalent (theoretical) zone areas of SV. Defocus measures of all samples throughout the natural pupil were then used to calculate the percentage of the pupil that contained myopic defocused light for each lens. Myopia was defined as -0.50 D or more myopia, and hyperopia +0.75 D or more hyperopia.

Results : At -0.25 D TV on average only 11.44% of the pupil was myopic with SV, whereas 62.44%, 84.23%, and 50.39% of the pupil was myopic for the DF, MF, and RB designs, respectively. At -4 D TV, all lenses exhibited a systematic decrease in the percentage of pupil area with myopic defocus (SV: 2.81%; DF: 18.05%; MF: 5.32% and RB: 26.33%), but more of the pupil remained myopic with the multizone lenses compared to SV.

Conclusions : Multizone lenses introduced significant amounts of myopic defocus at all viewing distances, however, the magnitude and proportion of defocus was influenced by the lens zone geometry along with viewing distance dependent changes in pupil sizes. Lens with the RingBoost^TM (RB) technology retained relatively higher levels of myopic defocus at near viewing.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Figure 1: Average percentage of pupil area with defocus at 4 target vergences.