Modelling the refractive and imaging impact of multi-zone lenses utilised for myopia control in children's eyes

Abstract

Purpose: To develop an optical model of a child's eye to reveal the impact of target distance and accommodative behaviour on retinal image quality when fitted with multi-zone lenses.

Methods: Pupil size, aberration levels and accommodative lag were adjusted for models viewing stimuli at 400, 100, 33 and 20 cm. Distributions of defocus across the pupil and simulated retinal images were obtained. An equivalent 16-point letter was imaged at near viewing distances, while a 0.00 logMAR (6/6) letter was imaged at 400 cm. Multi-zone lenses included those clinically utilised for myopia control (e.g., dual-focus, multi-segmented and aspherical optics).

Results: Viewing distance adjustments to model spherical aberration (SA) and pupil radius resulted in a model eye with wider defocus distributions at closer viewing distances, especially at 20 cm. The increasing negative SA at near reduced the effective add power of dual-focus lenses, reducing the amount of myopic defocus introduced by the centre-distance, 2-zone design. The negative SA at near largely compensated for the high positive SA introduced by the aspheric lens, removing most myopic defocus when viewing at near. A 0.50 D accommodative lag had little impact on the legibility of typical text (16-point) at the closer viewing distances.

Conclusions: All four multi-zone lenses successfully generated myopic defocus at greater viewing distances, but two failed to introduce significant amounts of myopic defocus at the nearest viewing distance due to the combined effects of pupil miosis and negative SA. Typical 16-point type is easily legible at near even in presence of the multi-zone optics of lenses utilised for myopia control and accommodative lag.

Keywords: aberrations; accommodation; defocus; multi-zone lenses; myopia; simulated retinal image.

FIGURE 1

Ex‐vivo, aberrometer measured power maps of four myopia control lenses. (a), (b) and (d) represent sagittal powers maps for MiSight 1 day, Biofinity Multifocal centre‐ systematically distance (CD) and NaturalVue Multifocal 1 Day contact lenses, respectively, whereas (c) represents the curvature power map of the peripheral region of a Defocus Incorporated Multiple Segments (DIMS) spectacle lens. The red and blue triangles on the colour bar scale indicates the measured distance and add power, respectively. Note that these measured powers served as the basis for optical modelling as opposed to the nominally labelled powers on the packaging

FIGURE 2

Impact of optics of an accommodating model child's eye. Defocus distributions at four target vergences (step size 0.125 D) employing different focusing strategies, are shown. Defocus equals refractive state minus target vergence

FIGURE 3

Impact of optics of an accommodating model child's eye. Point Spread Functions (PSF) and simulated retinal images of letter E computed for different viewing distances and employing different focusing strategies are shown as mentioned at the top. For each strategy, the effect of typical lag (0.50 D) is shown

FIGURE 4

Impact of adding a MiSight 1 day contact lens to the accommodating model child's eye. (a) Schematic of a model child's eye wearing a dual‐focus contact lens, showing focal planes for the distance correction and add (treatment) zones when viewing a near target. Defocus distributions using (b) distance focus at four different target vergences and (c) treatment zone focus at two near target vergences are shown. For treatment zone focus, the data has shifted by the lens specified +2.00 D of additional power. Defocus equals refractive state minus target vergence

FIGURE 5

Impact of adding MiSight 1 day contact lens to the accommodating model child's eye. Point Spread Functions (PSF) and simulated retinal images of a letter E are computed for different viewing distances for a model eye focusing either the distance zone or treatment zone as mentioned at the top. For distance zone focus, the effect of typical lag (0.50 D) is also shown

FIGURE 6

Impact of adding a Biofinity Multifocal centre‐distance (CD) contact lens to the accommodating model child's eye. Defocus distributions using (a) distance focus at four different target vergences and (b) add zone focus (assuming +1.10 D add) at two near target vergences are shown. Defocus equals refractive state minus target vergence

FIGURE 7

Impact of adding a Biofinity Multifocal centre‐distance (CD) contact lens to the accommodating model child's eye. Point Spread Functions (PSF) and simulated retinal images of a letter E are computed for different viewing distances using distance zone focus and add zone focus as mentioned at the top. For distance zone focus, the effect of typical lag (0.50 D) is also shown

FIGURE 8

Impact of adding Defocus Incorporated Multiple Segments (DIMS) spectacle lens to the accommodating model child's eye. Defocus distributions at four different target vergences are shown for the model eye with minRMS focus of the distant optic and viewing through peripheral optics (assuming +3.50 D add), obtained by: (a) sagittal method and (b) local curvature method to compute power. The inset at the top (a) represents the geometry of the DIMS spectacle lens with the arrowhead pointing to its peripheral optics, at the bottom (b) is the curvature power map of the peripheral optics. Note the different range of y‐limits in (a) and (b) for better data visualization

FIGURE 9

Impact of adding Defocus Incorporated Multiple Segments (DIMS) spectacle lens to the accommodating model child's eye. Point Spread Functions (PSF) and simulated retinal images of letter E are computed for the model eye with minRMS focus of the distant optic and viewing through either the (a, b) central or (c, d) peripheral optics, with and without the effect of typical lag (0.50 D) as mentioned at the top

FIGURE 10

Impact of adding a NaturalVue Multifocal 1 Day contact lens to the accommodating model child's eye. Defocus distribution at four different target vergences employing different focusing strategies are shown. Defocus equals refractive state minus target vergence

FIGURE 11

Impact of adding a NaturalVue Multifocal 1 Day contact lens to the accommodating model child's eye. Point Spread Functions (PSF) and simulated retinal images of a letter E computed for different viewing distances and employing different focusing strategies are shown at the top. For each refractive strategy, the effect of typical lag (0.50 D) is shown