In order to provide reference for clinical application, the normal values of retinal blood flow parameters in Chinese healthy children were measured by oct-angiography. Meanwhile, the repeatability and consistency of retinal blood flow parameters measured by oct-angiography in children were further analyzed, and the correlation of retinal blood flow parameters with eye axis, choroidal thickness, age and diopter was analyzed, so as to provide basis for clinical diagnosis of children's ophthalmopathy. Objective to study the effect of short-term optical defocusing on retinal blood flow parameters, and analyze the correlation between the changes of posterior segment parameters before and after short-term optical defocusing, so as to provide the basis for the possible compensation mechanism of posterior segment optical defocusing, and further understand the possible physiological mechanism of myopia.

Inclusion Criteria:

1. The subjects should be 6-18 years old, with parents' consent and be able to abide by the experimental rules;
2. uncorrected visual acuity or spectacle corrected visual acuity ≥ 1.0, and each eye can fix the target;
3. equivalent spherical lens range + 0.50D ~ - 6.00D, binocular spherical lens anisometropia ≤ 1D, anisometropia ≤ 1.5D;
4. frame glasses can be worn for patients with ametropia, and hard contact lenses can not be worn for at least 4 weeks, and anisometropia can not be worn for 2 weeks
5. intraocular pressure in the normal range (9mmhg-21mmhg)

Exclusion Criteria:

1. Patients with history of ocular trauma and surgery;
2. patients with ocular organic lesions or systemic diseases;
3. patients with dry eye;
4. patients in the treatment period using drugs (such as atropine eye drops);
5. patients with poor cooperation or unqualified image quality

Children volunteers with normal corrected visual acuity