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Noel A Brennan, Michael J Collins, Xu Cheng; Design Concepts for a Myopia Control Soft Contact Lens. Invest. Ophthalmol. Vis. Sci. 2022;63(7):1438 – F0396.
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© ARVO (1962-2015); The Authors (2016-present)
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.
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.
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.
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.
Illustrative composite images for DF lenses comprising equal area contribution from DZs and MCTZs.
Ray tracing and point spread at the retina for (a) DF design, (b) DF design with higher MCTZ plus power, (c) a torus MCTZ producing a ring focus (d) torus MCTZ design with higher MCTZ plus power.
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