At the completion of this article, the reader should be able to improve their knowledge of emerging myopia control interventions, including:
- Understand the mechanisms behind light therapy’s effects on axial eye growth.
- Evaluate the effectiveness of repeated red light therapy (RRL) in slowing myopia progression.
- Advise patients on balancing increased outdoor activity with sun safety practices to prevent myopia.
- Understand the potential of various light therapies as emerging interventions for myopia management.
Dr Emily C. Woodman-Pieterse
PhD, FAAO, FHEA
Centre for Vision and Eye Research,
Queensland University of Technology
Dr Rohan P.J. Hughes
PhD, FAAO, AFHEA
Centre for Vision and Eye Research,
Queensland University of Technology
Light therapy is a rapidly expanding field in myopia intervention, with multiple promising options on the horizon. QUT’s DR EMILY WOODMAN-PIETERSE and DR ROHAN HUGHES expect they will become adjunctive therapies to complement current interventions. But what do optometrists need to know now?
Light therapy is delivered by a device that emits a controlled light dose, commonly applied in the treatment of dermatological conditions and mood and sleep disorders. Following the discovery that outdoor light exposure can influence refractive error development and eye growth,1 interest in light therapy as a potential intervention for myopia control has surged.
Epidemiological evidence suggests that the lowest incidence and prevalence of myopia in childhood are associated with the greatest amount of outdoor activity.1
Although the characteristics of the outdoor environment responsible for this protective effect are unclear, the higher intensity and/or the broader spectral distribution of sunlight are the most likely culprit and are absent in indoor environments.2
While recommending that young, at-risk patients spend more time outdoors is a safe, simple and affordable solution with additional health benefits, this may not be practical in all locations and climates, and as such, light-based interventions – such as repeated red light therapy, violet/ultraviolet (UV) light therapy, blue spot stimulation and enhanced indoor lighting designs – have emerged as potential treatments to complement existing myopia control interventions.3
Animal studies suggest that chromatic cues within light can modulate axial eye growth and refractive error development, driven by the eye’s inherent longitudinal chromatic aberration.4In some animal models, those reared under short (blue and violet) wavelengths developed less myopia than those raised under long (red) wavelengths, consistent with eye growth changes predicted by longitudinal chromatic aberration (Figure 1).
However, some primate studies have been contradictory, with longer wavelengths found to slow eye growth. These findings have inspired the use of light therapy to limit myopia development and progression in children using a variety of wavelengths.3
Outdoor Time
While the ideal timing and intensity of outdoor light is still being determined, evidence suggests children at high risk of myopia should be encouraged by their eyecare provider to aim for two to three hours per day (or 14-21 hours per week) outdoors to reduce their odds of developing myopia.5
Randomised controlled trials conduced in Chinese and Taiwanese schools, in which children were allocated additional outdoor time (such as additional daily sessions of outdoor activity, enforced outdoor play during recess, and incentivised outdoor activities on weekends for students and their families) have found significantly lower myopia incidence, axial eye growth and myopic refractive shifts in non-myopic children.1, 3 However, the benefits for children who are already myopic are smaller and clinically insignificant.1
Sun Safety
While the aim of myopia control is to reduce the long-term risk of pathological myopia development and vision impairment, practitioners should be aware that the potentially sight- and life-threating complications of excessive UV radiation exposure should be of equal concern.
Although diseases associated with excessive UV exposure to the skin and eyes do not typically manifest until adulthood, the damage is sustained primarily in childhood when the melanocytes in juvenile skin are more susceptible to DNA damage.6
Myopia control messaging must also emphasise the importance of sun safety measures, with research suggesting that even when wearing sunglasses, hats, or seeking shade outdoors, light levels are still above the threshold illuminance for myopia prevention.7
Classroom Lighting
Since two-to-three hours a day outdoors may not be possible for all, improvement of indoor lighting, particularly in classrooms, may be a viable alternative for large-scale implementation. Select primary schools in China have participated in classroom-based lighting intervention studies, where either illuminance levels8 or spectral composition of light sources9 have been altered to more closely resemble outdoor environments.
Traditionally lit classrooms in China have an average luminance of 74 lux, but in schools that redesigned their lighting to ensure a minimum desktop illuminance of 300 lux, the incidence of new myopia fell from 10% to 4% over 12 months.8 Similarly, in schools that introduced artificially synthesised light sources to mimic the spectrum of daylight, myopia incidence decreased by 5% in seven to nine year-old children over three years.
While these interventions have produced small but significant reductions in cases of new myopia, they have failed to slow progression in children with established myopia. As with outdoor light programs, practitioners may find that children at high risk for myopia onset gain the most benefit from modified indoor lighting.
Repeated Red Light Therapy
Repeated red-light (RRL) therapy has gained significant interest in recent years, with the greatest volume of clinical trial data and most promising evidence supporting myopia control efficacy of the light therapy options.3
While numerous RRL therapy devices have been used overseas, only one has been approved by the Therapeutic Goods Administration for use in Australia: the ‘Myopia Management Device’ (Eyerising International). This is a home-based, desktop device that delivers red light via a semiconductor laser with a peak wavelength of
650nm and illuminance levels of approximately 1600 lux through the pupil. Treatment is administered twice daily for three minutes each session (a minimum of four hours between sessions), five days a week.
Systematic reviews and meta-analyses have concluded that RRL therapy may be effective in slowing eye growth and myopia progression,3,10 with treatment effects detected from four weeks to 24-months after commencement. However, only one study to date followed participants for longer than 12 months.11
Given that myopia typically progresses for many years in childhood before stabilising in late adolescence/early adulthood, studies of longer duration are required to support widespread adoption of RRL therapy. Additionally, it appears there is moderate rebound on cessation, although not enough to completely eliminate all benefit gained from the 12-month treatment period.11 If the treatment effects are not sustainable, the clinical utility of this treatment is limited.
How does red light therapy work?
There are multiple theories as to how RRL therapy thickens the choroid and slows eye growth. The prevailing theory is that red light of a specific wavelength (~650 nm) may increase cellular energy production and nitric oxide release that either increases choroidal blood flow and oxygenation and reduces scleral hypoxia, or stimulates the production of scleral collagen and fibroblasts, both of which are thought to strengthen the sclera and reduce axial eye growth (Figure 2).
There has been some suggestion that the choroid may be thickening in response to the high energy levels emitted from these instruments, which may be causing retinal toxicity or altering chorioretinal metabolism.12 There have been no serious device-related adverse events reported in the clinical trials conducted, however, a case has been reported of a 12-year-old girl who sustained outer retinal damage, similar in appearance to laser-induced maculopathy, after five months of RRL therapy (once treatment was terminated, the patient partially recovered over a period of three months).13
To enable widespread adoption of RRL therapy as a safe and effective option for myopia control, future clinical trials will require comprehensive assessments of retinal structure and function beyond visual acuity measurements and macular OCT, such as multifocal electroretinography and high-resolution imaging of photoreceptors and other retinal cells.
Recently, the Chinese government has changed the regulation of RRL devices which will have implications for future study of its effectiveness and safety, and may impact the adoption of RRL treatments.14
Blue Light ONH Stimulation
Blue light (peak wavelength ~480 nm) has been found to activate the melanopsin photopigment located within the human eye, likely in a similar manner to sunlight. Melanopsin is contained within the cell bodies, axons and dendrites of the intrinsically photosensitive retinal ganglion cells (ipRGCs), a small subset of retinal ganglion cells that are thought to be responsible for the light-mediated mechanisms that regulate eye growth and myopia development (Figure 3).2
The axons of the ipRGCs converge at the optic disc and form the optic nerve, so that the highest density of melanopsin exists within the region of the optic nerve head. Optic nerve head stimulation with a small, circular patch of blue light allows for maximum ipRGC stimulation that, in turn, stimulates retinal amacrine cells to release dopamine and slow eye growth, while avoiding rod and cone pathway activation within the retina that may inhibit dopamine release.15 An additional benefit of this targeted light therapy delivered to the optic nerve head is that the absence of rods and cones means the light stimulus is virtually undetected by the wearer during the treatment.
A digital application – MyopiaX (Dopavision GmbH) and associated hardware have been developed, delivered via a standard smartphone inserted into a virtual reality (VR) headset, which allows simultaneous bilateral blind spot stimulation while the wearer plays a video game controlled using a Bluetooth gaming controller.15 There are several interactive, age-appropriate games available via the MyopiaX app designed to engage the child and stabilise their gaze during the treatment (~10-minutes per session, twice per day), allowing
for reliable blind spot stimulation.
A randomised, controlled, multicentre clinical trial of the MyopiaX in Europe has recently concluded, in which children were assigned to use the MyopiaX app while axial eye length, choroidal thickness, refractive error, and safety measures were monitored over a 12-month period and compared to children wearing myopia control spectacles (ClinicalTrials.gov ID: NCT04967287). While the longer-term clinical trial data on efficacy and safety is yet to be published and established, short-term studies have demonstrated that blue spot stimulation can improve contrast sensitivity, increase electrical retinal activity, thicken the choroid and shorten axial eye length, which suggests that longer-term use may have the potential to slow myopic eye growth.15
Cyan Light
Based on the knowledge that some intrinsic properties of sunlight influences refractive error development, some studies have investigated whether exposure to cyan light (peak wavelength ~500 nm), which falls within the spectral sensitivity of melanopsin, could reduce myopic eye growth via the melanopsin-ipRGC signalling pathway (Figure 3).16,17
The effect of short-term use of low-powered LEDs emitting cyan light, via both commercially available (Re-timer Pty Ltd)16 and experimental frame designs,17 have been investigated in children and adults. Both studies showed that cyan light had the potential to cause significant choroidal thickening, either through exposure to 30-minutes of light therapy each morning for one week16 or one single two-hour session of exposure, which was also accompanied by axial eye shortening.17
Given that these short-term ocular changes have been shown to serve as a biomarker for longer-term slowed eye growth, it has been speculated that similar devices could be used for myopia intervention following further research and development. While the Re-timer device is commercially available for the treatment of sleep and circadian rhythm disturbances such as jet lag, insomnia and seasonal affective disorder; it should not be used for the purpose of myopia control unless evidence of efficacy in large scale clinical trials becomes available.
Violet Light
Violet light (360-400 nm) is abundant in daylight and outdoor environments, but almost entirely absent indoors. Windows, car windshields, and ordinary spectacle lenses and contact lenses block violet light, and fluorescent, incandescent, and LED sources irradiate no violet light. This prompted a Japanese research group to investigate whether violet light can slow progression in primary school aged children who were already myopic.18 Children wore custom-built, 3D-printed frames that emitted violet light for three hours each day between 11:00am and 2:00pm, over a three-month period, after which significant reduction in eye growth and refraction progression was reported in some of the age-groups tested.
Compared to red light therapy, very few studies have investigated violet/UV light on myopia prevention and control, sample sizes have been relatively small, and the evidence available shows much more modest treatment effects.3 Although no adverse events have been reported in these violet light clinical trials, the longer-term risks of excessive UV light exposure are well known, and require consideration with respect to these devices.
Conclusion
Light therapy is a rapidly expanding field in myopia intervention, with multiple promising treatment options on the horizon, such as RRL therapy, blue light optic nerve head stimulation, and violet light glasses. It is expected that, in coming years, as more safety and efficacy data become available for long-term use of these devices, they will become popular adjunctive therapies to complement currently available myopia control treatments.
In the meantime, outdoor time recommendations should be included in all management discussions in established or emerging myopic children. Equally as important, practitioners must emphasise that increased sunlight exposure must be accompanied by sun safety strategies, such as sunglasses and hats, and seeking shade outdoors.
More reading
Repeated low-level red-light therapy: a guide for clinicians
Myopia – will Australia sink or swim in surging global wave?
This Australian optometrist is prescribing plano defocus lenses to prevent myopia
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