Which layer of the eye is rich in blood vessels and nourishes the retina?

The choroid layer of the eye plays a critical role in nourishing the retina due to its rich supply of blood vessels. Located between the retina and the sclera, the choroid provides essential nutrients and oxygen to the retinal tissue, which is vital for maintaining the health and function of the photoreceptor cells responsible for vision.

This vascular layer also contains melanin, which helps absorb excess light and reduces glare, enhancing visual acuity. By effectively supplying blood, the choroid supports the metabolic demands of the retina, which is particularly important because the retina is one of the most metabolically active tissues in the body.

The sclera, while also part of the overall structure of the eye, primarily provides mechanical support and protection, not nourishment. The cornea is primarily responsible for focusing light and has no blood vessels; it receives nutrients from the tear film and aqueous humor instead. The iris, which is responsible for controlling the amount of light entering the eye, does not have the same vascular function as the choroid. Thus, the choroid is uniquely suited for nourishing the retina, making it the correct choice in this context.