Juan Ding, OD, PhD

There have been so many recent studies on this ‘novel’ treatment and I have to write about it now.

First of all, what is this treatment?

The official name is ‘repeated low level red light’. It was originally used by Chinese ophthalmologists to treat amblyopia, though there was hardly any evidence for it.

For myopia control, the red light that is used in the treatment has a wavelength of 650 nm, with 1600 lux through the pupil, and children are supposed to look at this light for 3 min x 2 per day, at least 5 days a week.

Is it a strong light? It seems so. A small number of subjects have to withdraw from these studies due to intolerance to the light. Many report after images, but most report the after images gone after 4 minutes.

If you think about it though, that is indeed a strong light. When do you ever experience after images up to even 1 minute in real life?

However, the energy that these devices emit to the retina for that treatment duration in theory is safe. Although that cannot be said to be true for all devices out in the market (see below on ‘issues and concerns’).

Does it reduce myopia progression?

A few years ago, Chinese ophthalmologists and researchers started using this device to slow myopia progression, and found it to be very effective. For example, in 2021, a multi-center, random and single blinded study recruited 264 myopic children 8-13 years of age and found that after 12 months of treatment, the red light group showed significant less myopic progression vs the control group [1].

This new therapy is attractive because it takes very little time per day to do it, perhaps just next to atropine eye drops, and it’s effective.

Any issues or concerns?

However, safety is a big concern. Indeed, there is a report about retinal damage of a child [2]. And a study shows that some of these devices actually exceed the safety limit for human retinas [3].

Another issue is that the follow up period for this treatment is usually short, about 1 year, and we don’t know if the effect is longer lasting, if the effect diminishes after longer duration of usage, or if it can be safely used for longer than 1, 2 or a few years.

Can you use it in children who are not yet myopic to prevent myopia from happening?

Further, can it be used to prevent myopia from developing in the first place? Low dose atropine seems to work [4], in addition to out door activities (so many publications on this). But will red light work too?

A study was published this month to show that the red light seems to reduce myopia incidence in premyopic children as well [5]. This study recruited premyopic children 8-13 years of age and randomly divided them into 2 groups, one control (36 children) and one receiving repeated red light therapy (40 children) 3 min x2 every day for 12 months. After 12 months, the control group showed an average of -0.52 D myopic shift and the treatment group showed -0.18 D shift. The axial length of control group was +0.29 and that of the treatment group was +0.15. The incidence of myopia was 19.4% after 12 months for the control group, and 2.5% for the treatment group. These results show a good efficacy of preventing myopia with the red light therapy. I have adapted the study data in the following figure (Figure 1).

Figure 1. Time courses of change of spherical equivalent refraction (A) and axial length (B). PM- C, premyopia- control group; PM- RL, premyopia RLRL group.

The study also included myopic children with control or red light therapy, and found that red light reduced myopia progression similar to previous studies. But I removed those lines to make it simple.

Axial length shortening

Another cool finding is that red light in some children caused a shortening of the axial length, and reduction in myopia in the first 3 months, then this effect gradually dwindled. Shortening of axial length is not commonly observed, but in certain myopia control cases, it is observed with atropine eye drops, orthokeratology lenses and peripheral defocus glasses. The red light treatment seems to have a large percentage of such shortening cases, which speaks for its good efficacy. Maximum AL shortening percentage was 53.1% in the myopic children who received red light at 3 months, and 21.9% of the subjects still had a significant shortening in AL after 12 months of treatment. In the premyopic children who received red light, maximum AL reduction was 22.5% at 3 months and 12.5% at 12- month follow- up (Figure 2).

Figure 2. The percentage of subjects showing significant AL shortening during the treatment. Axial length (AL) shortening (>0.05 mm) was defined as a significant shortening. PM- C, premyopia- control group; PM- RL, premyopia RLRL group.

Conclusion and final remarks

Recently several studies have shown that repeated low level red light therapy is effective and safe for myopia control and prevention, for the short follow up period of 12 months. Its efficacy is quite impressive, however, we wait for the longer time follow up studies of efficacy and safety.

I don’t view this as a first line treatment of myopia control or prevention, but for those unresponsive to atropine, orthokeratology, soft multifocal contact lenses and peripheral defocus glasses, this is worth trying.

What I would like to see in future studies is a dose response of this treatment. When atropine came out, carefully designed studies looked at all possible concentrations and landed us some pretty safe doses. The red light has just one intensity, one set of treatment dose and it’s used in all studies. Since the safety is the obvious elephant in the room, why not address it? Why not design studies to look at lower intensity, lower treatment duration and frequency? If there is treatment efficacy at half the intensity and even less duration and frequency, we want to know.

Another burning question is that no one knows why the red light works. Is there any intrinsic benefit of redness of the light? Or is it just intensity of the light? We all know out door activity is effective largely due to the brighter light outside. So why not design a real control group where the kids will look at another light source of 1600 lux, perhaps a white light, perhaps a green light, to find out if red light is truly sacred in myopia control? If it’s all about delivering light energy to the retina, then blue light will work even better, right? These studies will help us better understand the mechanism of this seemingly magic treatment.

References:

[1] Jiang, Y., et al., Effect of Repeated Low-Level Red-Light Therapy in Myopia Control in Children: A Multicenter Randomized Controlled Trial. Ophthalmology, 2021.

[2] Liu H, Yang Y, Guo J, et al. Retinal damage after repeated low- level red- light laser exposure. JAMA Ophthalmol 2023;141:693–5.

[3] Ostrin LA, Schill AW. Red light instruments for myopia exceed safety limits. Ophthalmic Physiol Opt. 2024; 44: 241–248. https://doi.org/10.1111/opo.13272

[4] Yam JC, Zhang XJ, Zhang Y, et al. Effect of Low-Concentration Atropine Eyedrops vs Placebo on Myopia Incidence in Children : The LAMP2 Randomized Clinical Trial . JAMA. 2023;329(6):472–481. doi:10.1001/ jama.2022.24162

[5] Liu G, Rong H, Liu Y, et alEffectiveness of repeated low-level red light in myopia prevention and myopia controlBritish Journal of Ophthalmology Published Online First: 17 April 2024. doi: 10.1136/bjo-2023-324260