The choroid is the middle layer of tissue in the wall of the eye. It’s found between the sclera (the whites of the eyes) and the retina (the light-sensitive tissue in the back of the eye).
The choroid forms the uveal tract, which includes the iris and the ciliary body.
The dark-colored melanin pigment in the choroid absorbs light and limits reflections within the eye that could degrade vision.
Melanin is also thought to protect the choroidal blood vessels against light toxicity.