The vascular tunic of the eye is the middle coat of the eyeball consisting of highly vascular and heavily pigmented connective tissue, according to class notes from Austin Peay State University. This tissue has a posterior choroid layer, an anterior ciliary body and an iris.
The choroid is the posterior, or back, portion of the eyeball that provides blood supply toward the back of the eye. The choroid also gives rise to the ciliary body and iris. The ciliary body is located between the choroid and the iris. It features a circular layer of muscles that help control the iris for the ability to focus. The iris is known as the colored part of the eye. It is also made up of muscles that control the size of the pupil, which adapts with the amount of light for better focusing, explains class notes from Austin Peay State University.