choroideus

Choroideus is a Latin adjective meaning “of the choroid” and is used in anatomical terminology to indicate structures associated with the choroid. In English, the term appears in the names of the ocular choroid and the brain’s choroid plexus, among other uses, and is typically rendered in the form choroideus choroidei or plexus choroideus in Latin texts.

In the eye, the choroideus oculi (the choroid) is the vascular middle layer of the eye located between the sclera and the retina. It provides oxygen and nutrients to the outer retina, helps absorb stray light to reduce scatter, and participates in heat management. The choroid is organized into layers including the suprachoroid, the stroma with blood vessels and melanocytes, and the choriocapillaris, a layer of capillaries that lies closest to Bruch’s membrane and the retinal pigment epithelium.

In the brain, the plexus choroideus (choroid plexus) is a highly vascularized structure formed by ependymal cells and underlying pia mater that projects into the brain ventricles. It produces cerebrospinal fluid (CSF) and contributes to the blood–CSF barrier. There are choroid plexuses in the lateral ventricles, the third ventricle, and the fourth ventricle, collectively maintaining CSF composition and turnover essential for central nervous system homeostasis.

Clinical relevance includes ocular choroid disorders such as choroiditis and conditions affecting choroidal circulation, as well as choroid plexus abnormalities and tumors that can alter CSF production. The term choroideus thus serves as a location-based descriptor for structures tied to the choroid in both the eye and the brain.