To evaluate the long-term efficacy and safety of red-light therapy for myopia control over 2 years, and the potential rebound effect after treatment cessation.

The Chinese myopic children who originally completed the one-year randomised controlled trial in the previous study were enrolled. Children continued or started to daily usage of red-light therapy were defined as the RL group, while those who stopped using red-light therapy and switched to single-vision spectacles (SVS) as well as those who continued to keep single-vision spectacles in the second year were both regarded as the SVS group. Red-light therapy was provided by an at-home desktop light device emitting red-light of 650 nm and was administered for 3 min at a time, twice a day. Changes in axial length (AL) and cycloplegic spherical equivalence refraction (SER) are to be measured and compared as well as the adverse effects including the rebound effect.

Red-light therapy has emerged as a novel myopia control treatment modality recently. A 12-month randomised controlled trial (RCT) conducted by our research team was thought to be earlier to evaluate the treatment of myopic children using red-light therapy. The trial demonstrated that PBM therapy was effective on myopia control, reducing axial elongation and spherical equivalence refraction (SER) progression 103% and 127% compared with single vision spectacle (SVS) over a 12-month period, respectively. The promising efficacy of red-light therapy has been further confirmed in other studies. In addition, satisfactory user acceptability and no unrecovered functional and structural damages were observed.

Myopia generally progresses throughout childhood and hence a study duration of 1 year is not sufficient to widely adopt the red-light therapy as a treatment strategy for myopia control. The sustainability of treatment efficacy, rebound phenomenon upon cessation of treatment, and potential risks and adverse effects in myopic children with longer-term PBM therapy, remain to be fully elucidated.

Thus, the aims of this post-trial follow-up study were to invite the participants to come back for a 24-month visit and to investigate the long-term efficacy and safety of continued red-light therapy as well as the potential rebound effect following red-light treatment cessation.

Interventions and visits All spectacle lenses were made for single focus with full correction for each subject as the first intervention throughout the whole procedure for both groups. PBM therapy was performed with a low-intensity laser (LD-A, Jilin LD Optoelectronics Technology, Jilin, China) with an irradiance of 0.35 ± 0.02 mW/cm2, a wavelength of 650 nm ± 10 nm, and illumination of approximately 400 lux on average at the first 12 month. At the second 12 months, non-randomized cohorts continued according to the willing to use the device from both groups. Once decided, those usage would be followed up for another 12 months for tracking the change of axial length as well as the change of refractive error. All the adverse effects and any harms are encouraged to report during the next 12 months' study.

Inclusion Criteria:

1. Clinical diagnosis of myopia;
2. Ages of 9~13 years old;
3. Must be with best corrected visual acuity ≥20/25 (decimal record);
4. Must be the subject in the previous study of 12-month red-light therapy of myopia;

Exclusion Criteria:

1. Clinical diagnosis of glaucoma or retinal lesions;
2. Clinical diagnosis of optic media lesions (e.g., central thick corneal scars, cataract);
3. Clinical diagnosis of optic nerve dysfunction;
4. Clinical diagnosis of amblyopia;
5. Must be eligible for follow-up.