Abstract
Purpose :
Increasing power in a myopia control treatment zone (MCTZ) of a multifocal soft contact lens can increase myopia control efficacy but negatively impact vision. The basis of vision compromise is explored with simple optical modelling and a novel approach to break the nexus between efficacy and vision.
Methods :
The impact of MCTZ power, size and position on visual acuity, contrast and haloes/ghosting were modelled. Optical designs featured annular MCTZs surrounding a central distance vision correction zone (DZ), typical of dual focus (DF) designs such as Acuvue® Bifocal and MiSight®. To overcome limitations of DF designs, the non-coaxial principle described by Yi et al. (ARVO, 2021) was applied to the annular MCTZ. This was tested empirically with an adaptive optics system.
Results :
Composite images comprising the clear image from the DZ and blurred images from the DF MCTZ are consistent with Davis et al (ARVO, 2021), showing VA worsening up to a power of +2 to +3 D and improving beyond that level, but with reduced contrast (Fig 1). Rays from a distant point source passing through the DF MCTZ form a halo at the retina (Fig 2), with increasing power in the MCTZ increasing the size of the halo. Convolving for edges shows that ghosting is a major vision limitation of DF designs, with MCTZ power being the main driver of ghost-image size. Forming the MCTZ from a torus rather than a spherical shape generates a ring focus, which can markedly reduce the halo effect (eg. from 3.3° ± 0.1 with a +10D DF MCTZ to 0.11° ± 0.04 with a +10D torus MCTZ). Adding positive power into the torus MCTZ results in short-term (30 min) reduction (± SD) of axial length comparable to that observed with a +3 D full-field lens (11.4 ± 6.2 µm vs 11.0 ± 8.8 µm, N=17 and 18 respectively, p=NS) while maintaining acceptable vision quality.
Conclusions :
This is the first optical characterization of vision compromise versus myopia control efficacy with DF lenses to our knowledge. While treatment efficacy of a myopia control soft lens is related to the local power in the MCTZ, the optical method by which treatment is delivered can have a major impact on the extent of vision compromise.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.