Final answer:
The choroid is the structure that contains the blood vessels which nourish all layers of the eye.
Step-by-step explanation:
The structure containing the blood vessels that nourish all layers of the eye is the choroid. The choroid is a layer of highly vascularized connective tissue providing a blood supply to the eyeball, particularly nourishing the outer retina. It is part of the vascular tunic which is the middle layer of the eye, also including the ciliary body and the iris. The ciliary body is a muscular structure controlling the shape of the lens for focusing light, but it does not serve as the primary nourisher of the eye's layers. On the other hand, the aqueous humor is a watery fluid in the anterior chamber and not associated with the nourishment of eye tissues.