This study is a randomized controlled trial based on outdoor activity interventions at specific time periods, involving preschool children aged 4 to 5 years. It compared the axial length and myopia incidence between the intervention group and the control group at the 6th and 12th months of the intervention to determine the effect of outdoor activities at specific time periods on the prevention of myopia in preschool children. Additionally, the study investigated the association between outdoor activities at specific time periods and axial length and myopia in preschool children.

Preschool children with insufficient outdoor activity during specific time periods from one kindergarten were assigned to the intervention group, while those from another kindergarten with insufficient outdoor activity during specific time periods were assigned to the control group. The intervention group received an additional 1 hour of outdoor activity during a specific time period on each school day, while the control group did not receive any intervention and continued their regular routine. The intervention lasted for one year.

Participants underwent multiple assessments after joining the study. These assessments took place at baseline, at the 6th month of the intervention, and at the 12th month.

Inclusion Criteria:

• Students and their families were informed and voluntarily participated in the study, with parents signing the informed consent form.
• Able to cooperate with eye examinations and questionnaires.

Exclusion Criteria:

• Communication barriers, unable to cooperate.
• Strabismus, amblyopia, or any other ocular or systemic diseases that may affect refractive development.
• Children currently using orthokeratology lenses or rigid contact lenses.
• Using other interventions (such as acupuncture, massage, medication, ear acupuncture, etc.) to control myopia, apart from school eye exercises.