The middle layer of the eyeball is rich in blood vessels, pigment, and smooth muscle cells. This layer is called the vascular layer, and it is also known as the uvea or uveal tract.

The vascular layer consists of three sublayers that are continuous with each other:

Choroid (Read more!) - the largest portion of the vascular layer (it comprises the posterior portion); consists of connective tissue and blood vessels, providing nourishment to the outer layers of the retina; it also contains melanocytes that produce melanin, which absorbs excess light, preventing light reflection and scattering within the eyeball;
Ciliary body (Read more!) - forms the anterior portion of the vascular layer; it is composed of two parts - the ciliary muscle (Read more!) and the ciliary processes (Read more!); the lens (Read more!) is attached to the ciliary body, and contractions and relaxation of the ciliary muscle control and alter its shape, adjusting it for near or far vision; the ciliary processes produce aqueous humor;
Iris (Read more!) - colored circular structure with a central aperture (pupil (Read more!)) that also forms the anterior part of the vascular layer; it is situated between the cornea (Read more!) and the lens (Read more!); it contains melanin that determines the eye color of an individual; the pupil is responsible for transmitting light and the size of its diameter is controlled by smooth muscle fibers within the iris (sphincter pupillae muscle and dilator pupillae muscle).

Unlock with Premium

Vascular layer of eyeball