The choroid is highly vascularized and contains a substantial blood volume, accounting for approximately 65% of the total blood supply within the eye. It receives its blood supply from the short posterior ciliary arteries and drains through the vortex veins. The capillaries within its inner layer have high permeability and provide nutrients to the outer layers of the retina. The permeability of the choroidal capillaries allows small molecules, such as fluorescein, to leak easily, while large molecules, such as indocyanine green dye, have limited leakage. This property enables better visualization of choroidal vessels in clinical imaging.
The choroid's rich blood supply contributes to temperature regulation within the eye. It also contains abundant melanin, which serves to shield the eye from excess light and functions as a "dark chamber," aiding in optimizing visual clarity.