The posterior portion of the vascular tunic, which appears black from melanin-containing pigment cells, is the ______.Multiple choice question.

The correct answer is choroid.

Explanation:

The vascular tunic of the eye is comprised of three main parts: the choroid, ciliary body, and iris. The choroid is the posterior part of the vascular tunic, and it contains a high concentration of blood vessels along with melanin-containing pigment cells. The purpose of the melanin is to absorb excess light, which helps to reduce reflection within the eye and improves visual acuity. This black appearance from the melanin plays a vital role in preventing light scattering, thus enhancing the overall efficiency of the retina's light reception. The choroid also supplies oxygen and nutrients to the outer layers of the retina, further supporting its function in vision.