The purpose of this clinical trial is to investigate the incidence and magnitude of axial length shortening after repeated low-level red-light therapy in high myopia children and teenagers.

High myopia has become a major public concern globally, which is characterized by excessive axial elongation of the eyeball. Axial elongation is accompanied by mechanical stretching and thinning of the choroid and sclera, causing vision-threatening complications. Repeated low-level red-light (RLRL) therapy is an emerging effective and safe therapy for myopia control. Previous clinical trials in China have observed clinically significant axial shortening after RLRL treatment.

The purpose of this study is to investigate and identify possible mechanism for axial length (AL) shortening after 12-month RLRL therapy in highly myopic children and teenagers aged 8-18 years. In addition to single vision spectacles, subjects will receive RLRL treatment at home under supervision of the parents/guardians according to a standard protocol. Axial length, visual acuity, cycloplegic spherical equivalent refraction, slit lamp, fundus camera and optical coherence tomography/angiography will be measured at 1-, 3-, 6- and 12-month follow-up visits.

Inclusion Criteria:

1. Provision of consent.
2. Age: ≥ 8 and ≤ 18 years at enrolment.
3. High myopia: cycloplegic sphere of -6.00 diopters (D) or greater in both eyes.
4. Willing and able to participate in all required activities of the study.
5. The children currently on myopia control treatment can be recruited if myopia control treatments (including but not limited to atropine, orthokeratology, rigid gas-permeable lenses, defocus spectacles, etc.) are discontinued for at least 2 weeks.
6. Normal fundus, tessellated fundus or with peripapillary diffuse chorioretinal atrophy.

Exclusion Criteria:

1. Secondary myopia, such as a history of retinopathy of prematurity or neonatal problems, or syndromic myopia with a known genetic disease or connective tissue disorders, such as Stickler or Marfan syndrome.
2. Pathologic myopia with signs of macula-involving diffuse chorioretinal atrophy, patchy chorioretinal atrophy, macular atrophy, lacquer cracks, myopic choroidal neovascularization or Fuchs' spots.
3. Strabismus and binocular vision abnormalities in either eye.
4. Previous any intraocular surgery affecting refractive status.
5. Other reasons, including but not limited to ocular or other systemic abnormalities, that the physician may consider inappropriate for enrolment.

Data will be shared as open data after proper anonymization.