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

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.

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).

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.

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.