Veins of orbit. (Central retinal vein not labeled, but region is visible - the vein is inside the optic nerve.)
Diagram of the blood vessels of the eye, as seen in a horizontal section. (Central retinal vein not labeled, but region is visible. The central retinal vein is at bottom running away from the retina through the optic nerve.)
The central retinal vein is formed by the convergence of veins that drain retinal tissue. The central retinal vein originates within the eyeball, emerging from the eyeball already as a single unified vein.[1]
The central retinal vein varies between individuals.[3] in some the central retinal vein drains into the superior ophthalmic vein, and in some it drains directly into the cavernous sinus.[3][4]
As the fluid surrounding the optic nerve within its meningeal envelope is contiguous with the cerebrospinal fluid of the central nervous system, increased intracranial pressure can cause compression of the central retinal vein where it emerges from the optic nerve (the accompanying artery is meanwhile less susceptible to compression due to its thicker arterial wall), with the resulting venous congestion causing oedema of the optic nerve (papilledema).[1]
Additional images
Interior of posterior half of bulb of left eye. The veins are darker in appearance than the arteries.