Effect of Different Wavelengths of Repeated Low-Level Light Therapy on Choroidal and Retinal Blood Flow Among Adults

Inclusion Criteria: 1. Age: 18-40 years at enrolment. 2. Healthy adults with best corrected visual acuity equal to or better than 1.0 in both eyes. 3. Provision of consent and able to participate in all required activities of the study. 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; or high myopia \< -8 diopters. 2. Strabismus and vision abnormalities (astigmatism \> 3.5 D) in either eye. 3. Refractive media opacity: corneal opacities, cataracts, or implanted intraocular lens, etc. 4. Ocular abnormalities that affect retinal function: macular degeneration, diabetic retinopathy, retinal detachment, glaucoma, or ocular hypertension, endophthalmitis, uveitis, optic neuropathy, etc. 5. Previous history of refractive surgery, intraocular surgery, laser therapy, and intravitreal injection, etc. 6. Systemic abnormalities: diabetes, hypertension, etc. 7. Drugs therapies with toxicity effects on the retina: hydroxychloroquine, etc. 8. Prior treatment of myopia control in the past three months including drugs, orthokeratology, progressive addition lenses, bifocal lenses, etc. 9. Other contraindications, including but not limited to ocular or other systemic abnormalities, that the physician may consider inappropriate for enrolment.