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HomemipatientBreaking the Nexus: Myopia Effect and Visual Acuity

Breaking the Nexus: Myopia Effect and Visual Acuity

One of the most significant developments in soft contact lens designs for myopia control in recent years promises both efficacy and visual acuity. This is what we’ve been waiting for, writes Dr Margaret Lam.

One of the most significant developments in soft contact lens designs for myopia control in recent years promises both efficacy and visual acuity. This is what we’ve been waiting for, writes Dr Margaret Lam.

At the recent World Congress of Optometry (WCO4), I was excited to hear Professor Noel Brennan, research fellow for Johnson and Johnson in Jacksonville, Florida, speak about what I believe is one of the biggest breakthroughs of the decade for myopia control.

Traditional contact lens designs used for myopia management have manipulated the image projected on to a patient’s retina by creating some form of simultaneous vision. Designs we are most familiar with include repurposed presbyopic contact lenses, a dual focus lens design, an aspheric progressive design, and an extended depth of focus design. Unfortunately for the patients, although slowing myopia progression, these designs have sometimes compromised visual acuity.

These lenses enable us to change the power of what a patient sees in the treatment zone, change the size of the treatment zone, or change the location of the treatment zone.

The Bifocal Lenses In Nearsighted Kids (BLINK) study1 established that we have ‘a dose response effect’ to these adjustments. A positive power effect in the periphery will increase the effect of protection against myopic progression. However, with increasing plus power, rays of light become more blurred through the treatment zone, causing central visual acuity to become more blurred. The patient will also experience ghosting and a ring of haloes in their vision.

As a result, there is a compromise: to reduce progression, patients must be prepared to tolerate a potentially, slightly negative impact on their visual acuity.

Prof Brennan referred to this as the “efficacyvision nexus” and it is something that he and his team have been working to overcome by developing an entirely new contact lens design – one that optimises efficacy while also optimising vision.

BREAKTHROUGH LENS DESIGN

Working with Queensland University of Technology researchers, Prof Brennan has experimented with putting coaxial and noncoaxial focus lenslets into contact lenses.

Essentially, coaxial focus lenslets converge into a single point of focus, whereas noncoaxial focus lenslets do not.

Studying the results of these two different foci provided the first novel breakthrough: Prof Brennan and his team found that non-coaxial design and coaxial design both effectively reduce axial length creating the same myopia control effect. Interestingly though, they found that coaxial focus lenslets reduced visual acuity and contrast sensitivity when compared with non-coaxial focus designed lenses; the latter achieved significantly better best corrected visual acuity, and better contrast sensitivity.

In fact, Prof Brennan concluded, a noncoaxial contact lens design increases treatment efficacy without compromising vision.

Furthermore, by introducing a torus to the design with a conic section, it was possible to create a prismatic and power effect, which redirects light (Figures 3 and 4).

Interestingly, Prof Brennan discovered that a non-coaxial contact lens design still requires the wearer to accommodate for near focus. Mechanistically, previous research suggests this is useful, as it is important for myopia control for a patient’s eye to continue to accommodate to read and focus up close.

Moving on from this work, Prof Brennan studied two different lens designs: Enhanced Efficacy (EE) and Enhanced Vision (EV) lenses against a dual focus lens, and against a conventional single vision distance spectacle lens control.

Published in Ophthalmology Science, he found that EE lenses showed significantly better protection against myopic progression when compared with single vision distance spectacles and dual focus lenses.2 The EV lenses showed similar effects in protection from myopic progression when compared with dual focus lenses, and delivered clearer visual acuity.

Studied in a 7.8mm central base curve, with an aspheric back surface and reduced excessive lens movement to optimise for a paediatric fitting, the EE design proved to be an efficacious lens design. Coupled with the fact that the EE lens was produced in an Oasys one day material – which contact lens practitioners know and feel confident with – this lens will add to our prescribing arsenal in myopia management when it becomes available.

Prof Brennan’s study had an enviable low drop out of 2% – perhaps due to the use of the Oasys material, which is well known for lens comfort and handling. Results from the ongoing study suggest that efficacy at the one-year mark is a reliable indicator of three-year outcomes.

THE PRACTICALITIES

Prof Brennan is, understandably, excited about the results of this work. Reporting on his research findings at WCO4 in Melbourne, he said, “We have built a myopia control contact lens from the ground up. We think this is the first time that this has happened. We have also had the first use of a novel apparatus to enable systematic concept optimisation and iterative refinement of individual lens designs. This is the first characterisation of the optical challenge of myopia control lenses.

“This is the very first application of noncoaxial optics in contact lenses to break the nexus between efficacy and vision. It is the very first use of a section of a torus, rather than a sphere, for use in the myopia control treatment zone,” he said.

“We have (United States Food and Drug Administration) FDA breakthrough device designation. The design concept was validated through clinical trials, and provided an excellent balance between efficacy and vision, resulting in lenses that meet all desired properties for paediatric myopia control.”

This is indeed an exciting new lens for eye care practitioners in Australia and New Zealand who are interested in myopia management. Being able to provide a solution for our patients with high risk of myopic progression, while simultaneously providing a higher level of visual clarity and less visual compromise, is something we have all been looking for. I can’t wait to find out more as Prof Brennan’s research advances.

Dr Margaret Lam is the National President of Optometry Australia. She practises optometry at 1001 Optical in Bondi Junction in Sydney, and teaches at the School of Optometry at The University of New South Wales as an Adjunct Senior Lecturer.

References

  1. Walline, J.J., Walker, M.K., Mutti, D.O., et al., Effect of high add power, medium add power, or single-vision contact lenses on myopia progression in children: The BLINK randomized clinical trial. JAMA. 2020;324(6):571–580. DOI:10.1001/jama.2020.10834.
  2. Cheng, M.D., Xu, J., Brennan, N.A., Randomized trial of soft contact lenses with novel ring focus for controlling myopia progression, Ophthal. Science. 18 October 2022 DOI: doi.org/10.1016/j.xops.2022.100232.