central vein of retina vs vena

central vein of retina and vena both are nouns.

Word	Noun	Adjective	Verb	Adverb
central vein of retina	Yes	No	No	No
vena	Yes	No	No	No

As nouns, vena is a hypernym of central vein of retina; that is, vena is a word with a broader meaning than central vein of retina:

central vein of retina: vein formed by the union of the retinal veins; accompanies central arteries of the retina in the optic nerve
vena: a blood vessel that carries blood from the capillaries toward the heart

Other hypernyms of central vein of retina include vein, venous blood vessel.

central vein of retina (noun)	vena (noun)
vein formed by the union of the retinal veins; accompanies central arteries of the retina in the optic nerve	a blood vessel that carries blood from the capillaries toward the heart