Abstract
Purpose :
Myopic defocus is considered a primary driver controlling myopia progression. Commercially available myopia control (MC) lenses incorporate positive powered lenslets in the treatment area and, through geometrical-based assumptions, are believed to produce a Net Myopic Defocus (NMD) at the retina. Utilising computer-based models and bench measurements we aim to verify the net focusing effect produced by several MC lenses.
Methods :
Three MC lenses (Essilor StellestTM and Hoya MiYOSMARTTM spectacles, and Coopervision MiSightTM contact lenses) with comparable proportions of geometrically determined treatment areas were analysed. Designs were optically simulated in Zemax (-1.0 D). Simulations were converted to a power map with an aperture of 30 mm for spectacle lenses and 5 mm for the contact lens. Power map data was analysed using Matlab software to characterise the power across the apertures of lenses but excluding the central optical zones for the spectacle lenses. The average power of a sample of individual treatment regions were measured using the NIMO wavefront power profiler (Lambda-X, Nivelles). Hyperopic powers were subtracted from myopic powers for the calculation of NMD. The MTF was measured on an anatomically correct physical model eye (on-axis for the contact lens and off axis through the treatment region for spectacles) over a range of object vergences (-2.0 D to +5.0 D in 0.1 D steps) using a 5 mm pupil. The results were compared with the corresponding simulation to verify validity.
Results :
The MTF confirmed good agreement between simulation and metrology (Figure 1). The MiSight lens showed a high NMD percentage for each analysis method (Table 1). However, both spectacles showed about equal distribution between myopic and hyperopic defocus in the optical analysis which differed substantially from the geometrical analysis of NMD where each treatment element is assumed to introduce only myopic focal points.
Conclusions :
The distribution of defocus found with computer modelling and bench measurements were different to conventional geometrical based assumptions in the spectacle lenses studied. The NMD is substantially less than previously understood and the presence of hyperopic defocus was similar to myopic defocus in these spectacle designs. Animal and clinical trials using myopia control lenses incorporating myopic defocus and basing hypotheses on a geometrical rather than optical NMD may need to be re-evaluated.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.