Final answer:
The choroid is what holds the retina against the pigmented layer of the eye; it is a part of the vascular tunic that supplies blood to the retina.
Step-by-step explanation:
The question pertains to the anatomy of the eye, specifically the part that holds the retina firmly against the pigmented layer. This role is fulfilled by the choroid, which is part of the vascular tunic and provides nourishment to the outer layers of the retina through its blood supply. The choroid, along with the sclera, forms the outermost layer of the eye's fibrous tunic. The sclera is known as the 'white of the eye' and continues with the cornea, the clear part that covers the front of the eye allowing light entry.
This anatomical structure is essential as the retina is where photoreception occurs; the cornea and lens refract light to focus images onto the retina, which are then processed into nerve signals for the brain to interpret.