(1) is rich in blood vessels, which can nourish the outer retina, lens and vitreous body. Choroidal diseases are caused by large flow and slow flow, and pathogens are easy to stay here. There are many small holes in the choroidal capillary wall, and fluorescein can leak from the choroidal capillary wall during fluorescence angiography.

(2) It is rich in pigment and has shading effect. (3) Lymphocytes and plasma cells exude during inflammation.