Rodenstock has launched a myopia control spectacle lens, adopting an asymmetrical defocus design covering the nasal and temporal zones.
The physiology involved in myopia progression is fascinating when you consider it. In essence, when corrected with single vision lenses, light is focused accurately on the central retina, but by default light then focuses behind the retina in the periphery. For some children, the body wrestles to bring those peripheral rays into focus. It’s adapting with good intentions, but in reality causes a spiralling feedback loop that causes the eye to elongate, compromising its fragile structures.
Myopia is projected to affect every second person within 27 years. It’s a major problem, but not insurmountable. That’s because ophthalmic lens companies are developing specially designed lenses adopting the concept of “peripheral defocus” to arrest eye elongation. This non-invasive approach cleverly refracts light in the periphery so that it hits in front of the retina while ensuring sharp central vision.
In April 2023, Rodenstock became one of the latest companies to launch a myopia control spectacle lens. There are various lens designs available for myopia control. Some companies rely, for example, on concentric rings focusing on all quadrants of the peripheral retina – superior and inferior, as well as temporal and nasal. Rodenstock is tackling this by use of another design approach.
The company’s lens – named MyCon – is a peripheral defocus lens but differs due to its horizontally asymmetrical design. It has a central vision zone, which provides stable refraction around the optical centre, while the outer areas create a peripheral progression along the horizontal meridian – temporal and nasal.
The lens has three distinct zones:
- A central zone, where the optical power corresponds to the wearer’s nominal refraction.
- A temporal zone of progressively increasing power up to 2.5 D.
- A nasal zone of progressively increasing power up to 2.0 D.
It’s a unique design, but Rodenstock Australia national sales and professional services manager Ms Nicola Peaper says several studies have demonstrated asymmetry of the peripheral retinal refraction in myopia, influencing the patented design (German patent DE 10 2009 053 467 B4) of the MyCon lens.
A highly regarded study was conducted by Dr Anne Seidemann, part of Rodenstock’s R&D team, with Professor Frank Schaeffel, a renowned myopia researcher at Germany’s University of Tübingen. In 2002 they demonstrated peripheral refraction and assumed that peripheral eye length varies in different parts of the retina.
“Rodenstock looks to be new to myopia control, but we’ve been instrumental in a lot of myopia research in Europe for over 20 years, which is one of those little-known things,” Peaper says.
Another study, by Faria-Ribeiro et al in 2013, showed differences of asymmetries in peripheral refraction and eye shape for different refractive groups and progressive and non-progressive myopes.
“Looking at progressing myopes in that study, we can see their retina is significantly different compared to non-progressing myopes, but within the non-progressing group it’s also different nasally to temporally; you’ve got more hyperopia nasally in the progressing than the non-progressing group,” Peaper says.
“Another interesting finding from studies is that the nasal retina has more ganglion cells and more cones responsible for fine vision, implying a neuro-functional dominance of the nasal retina (Curcio et al., 1990; Curcio & Allen, 1990). There’s a school of thought that if you have a greater density of ganglion cells and cones, then you’re getting maybe more signals for eye growth in that area. At Rodenstock, we’re saying it’s important to look at the horizonal meridian at the retina in progressing myopia. Therefore, we are concentrating our efforts nasally and temporally.”
Clinical effectiveness
While there isn’t a direct study of the MyCon lens, Rodenstock cites an independent clinical study by Tarutta et al conducted over five years (2012-2018) on a lens based in similar principles in children.
The study monitored myopia progression of a group of 146 Caucasian boys and girls, with myopia varying between -1.00 and -6.00 D. Participants were divided into two groups with the same average age of 10.5 years.
The first experimental group consisted of 94 participants (aged 7-14 years) who used lenses based on the principles of MyCon lenses, while the second control group consisted of 52 participants (aged 8-14 years) who used normal single vision lenses.
The study was conducted by the Helmholtz National Medical Research Centre for Eye Diseases of the Russian Ministry of Health, with myopia progression (mean power and axial length) assessed after six months, 12-18 months, two years, three years, and four to five years from the start of lens wear.
“And the results show that the control group became 40% (spherical equivalent [D]) more myopic over five years,” Peaper says.
“In terms of axial length, eye elongation in the treatment group was reduced by up to 56% after two years and 35% after four to five years when compared to the control group.”
Why is treatment important now?
Since announcing that Rodenstock will be offering a myopia control lens, Peaper has been overwhelmed, yet unsurprised, at the huge interest among Australian practitioners. After all, myopia control lens market penetration will likely pale in comparison to other products like progressive lenses.
But it ultimately comes down to the fact that optometrists now realise that single vision lenses are no longer an adequate response to progressing myopia.
While a standard minus single vision lens creates a divergence of light, forming a sharp image on the centre of the retina, it also projects light that is coming from the periphery behind the peripheral retina, which may trigger some children’s eyes to adapt and become excessively long, which increases myopia.
“If you are correcting using a spherical single vision lens, you are highly likely to induce very rapid eye growth, so we require a lens that focuses in the periphery in front of the retina. With Rodenstock’s MyCon lenses, it’s like thinking of a multifocal that starts with your distance script in the centre and then has progressive plus power horizontally to the outer edge. The nice thing is you still have your distance script vertically, so there’s a chance it’ll perhaps be easier to tolerate.”
It’s well documented myopia is one of the world’s biggest public health problems. This is because it’s predicated 50% of the world’s population will suffer from myopia by 2050, a staggering projection revealed by the Sydney-based Brien Holden Vision Institute in 2016.
Approximately 20% of children in Spain or Irish teenagers are affected, reaching much higher prevalence of about 50% in Chinese urban teenagers to almost 90% in older Chinese urban teens. From 2006 to 2011, the myopia prevalence in Australia rose from 11.5% to 18.9%. Today, the rate for Australia and New Zealand is estimated to be 36%, with the forecast rate by 2050 an estimated 55%.
In myopia, there are aetiology, genetic, behavioural, gender and environmental factors at play. For example, it’s well documented that the Asian population is at greater risk, while a child with two myopic parents has a 35 to 60% risk of also being myopic. However, this risk is reduced (25-40%) when only one of the parents is myopic. Females are also at greater risk.
“What’s worrying is that if you take all of these elements into account, there shouldn’t be the rise in myopia that we’re seeing,” Peaper adds.
However, there are steps that families can take to protect their children, such as reducing near work activities and increasing outdoor time. Wildsoet et al in 2019 concluded at least 80 to 120 minutes outdoors had preventive effects against myopia development, with Sherwin et al in 2012 showing every additional one hour of outdoor time per week linked with a reduction in the risk of myopia by 2%.
In light of this evidence, Peaper says there’s a need to educate parents about the impact of near work activities and outdoor time, as well as interventions available that slow progression.
“When we’re talking about controlling myopia, one of the major things we should care about is the magical number of -5.00 D, the threshold of high myopia,” she says, noting while around 900 million people will suffer from high myopia in future.
“Once you hit that, you’re 20 times more likely to get a retinal detachment – and once you reach -7.00 D, you’re about 120 times more likely to get myopic maculopathy. In other words, in the worst case you can lose your central visual acuity and become blind. If we can prevent people from progressing beyond -5.00 D, then ethically, we have to try and do something.”
Furthermore, Australia is expected to have 4.1 million high myopes by 2050, unless myopia management is implemented universally. These forecasts highlight the scale of the problem that is facing eyecare professionals given Australia in 2020 had an estimated 1.1 million, and New Zealand over 200,000, high myopes.
Dispensing the lens
Rodenstock MyCon lenses are available in index 1.5, 1.6, 1.67, and 1.74, which make the lenses both thinner and sleeker than many other myopia lenses on the market and well suited to high prescriptions.
Peaper says this is possible because the company grinds the lens on the back surface, rather than using moulds on the front surface. This also helps children who are potentially hesitant about wearing glasses because they are unhappy with the look.
According to Rodenstock, MyCon lenses are also well-suited for high prescriptions while also offering shock-resistance and high image quality. Practitioners can also choose the lens material to recommend to customers, with a wide range of available lens coatings available.
The adaption period is generally short, in a few cases up to two weeks.
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