The importance of myopia control soft contact lens design
In this article:
Paper Title: Design Concepts for a Myopia Control Soft Contact Lens
Authors: Noel Brennan (1), Michael Collins (2), Xu Cheng (1)
- Johnson and Johnson Vision
- Queensland University of Technology
Date: May 2022
Reference: ARVO Meeting 2022, Denver
Since increasing the power of the myopia control treatment zone (MCTZ) of a multifocal soft contact lens can negatively impact vision, this study utilized optical modeling to explore this relationship. The impact of power, size and position of MCTZ of a multifocal soft contact lens on visual acuity, contrast and haloes/ghosting was investigated. Optical designs featured annular MCTZs surrounding a central distance vision correction zone, typical of dual focus designs such as Acuvue Bifocal and MiSight.
The results demonstrate that visual acuity worsens up to a power of +2 or +3D and improves beyond that level, but with reduced contrast. Haloes increase with increasing power of the MCTZ, making this a major vision limitation in these designs.
In increasing technicality, a torus shape rather than spherical shaped MCTZ generated a ring focus which markedly reduced the halo effect. This torus shaped design also provided a short-term (30 min) reduction in axial length when worn for 30 minutes, more so than that provided by a full field of +3 defocus, and maintained acceptable vision quality.
What does this mean for my practice?
This study demonstrates that the optical design of dual focus contact lenses has a major impact on vision quality, with higher treatment zone powers leading to greater vision compromise. A torus shaped MCTZ can reduce the severity of visual compromise in comparison to a spherically shaped MCTZ.
This highlights the importance of optical design of myopia control contact lenses, as it can influence both efficacy and visual performance.
What do we still need to learn?
The novel design described requires further long-term research in terms of clinical outcomes for efficacy and vision outcomes, especially in comparison to other designs.
Title: Design Concepts for a Myopia Control Soft Contact Lens
Authors: Noel Brennan, Michael Collins, Xu Cheng
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 ghostimage 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.
Conclusion: 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.
Meet the Authors:
About Clare Maher
Clare Maher is a clinical optometrist in Sydney, Australia, and a third year Doctor of Medicine student, with a keen interest in research analysis and scientific writing.
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