This prospective observational study aims to understand the effects of different subaxial body positions on choroidal and retinal blood vessel density. The main questions it aims to answer are as follows:1) How do retinal and choroidal blood vessels adjust and repair after changes in body position?2) Is the change of body position related to the factors that cause myopia？ 3) Are there any differences in the regulation ability of fundus blood vessels in people with different ocular axes under the condition of changes in body position?

This project will use the wide field swept-source optical coherence tomography angiography, combined with data analysis and mining methods, to explore the self-adjustment and change mode and mechanism of retinal and choroidal blood vessels in the case of posture changes in an all-round and multi-angle way. There would be three kinds of postural changes, one is 15° head-up position, one is supine position, and the other is 15° head-down position. Relevant ophthalmological measurements would be performed before and after the postural changes. The objective is to discover the three-dimensional change mode of retinal and choroid blood vessels in different postures and compare the differences among people with different lengths of ocular axes, and to elucidate the relationship between the mode and ability of retinal and choroidal blood vessels to adjust and repair changes after changes in body position and myopia, to provide more ideas and objective basis for the occurrence and development of myopia, and lay a foundation for further research. It is of great significance to innovate the pathogenesis of myopia, deepen the theoretical understanding, and guide the prevention and control of myopia.

Inclusion Criteria:

1. Corrected visual acuity ≥1.0 (international standard visual acuity chart);
2. Age 10-40 years old;
3. In good health;
4. Give informed consent and volunteer for the study. The process of obtaining informed consent complies with GCP regulations.

Exclusion Criteria:

1. Can not cooperate with the completion of relevant inspection and data collection;
2. Pregnant and lactating women;
3. Patients with amblyopia, glaucoma, retinitis pigmentosa, senile macular degeneration, retinal artery obstruction, retinal vein obstruction, diabetic retinopathy and other eye diseases that may affect the blood circulation and vascular diameter of the retina and vein, or those who have undergone intraocular surgery;
4. Patients with cardiovascular and cerebrovascular diseases, endocrine diseases, autoimmune diseases;
5. Long history of smoking and drinking;
6. History of ocular trauma;
7. The mentally ill;
8. Those who have taken drugs that affect blood circulation in the past 3 months;

Healthy people in Chengdu City will be recruited through advertisement, and those who meet the inclusion and exclusion criteria will enter the study.