The optic nerve (cranial nerve II) is the cable from the back of each eye to the brain: it leaves the eyeball at the optic disc, runs back through the eye socket (orbit) and the optic canal of the skull, and joins its partner at the optic chiasm under the front of the brain. It carries everything the retina sees. [1]
On this model each optic nerve runs from the eye socket back to the chiasm; the eyes themselves are not in the model, so the nerve’s front end stops where the eyeball would be. [2]
The 3D brain needs JavaScript. The text below still says where the optic nerve is and what it does.
Slice
Opens cut by a top (axial) slice through the optic nerve. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
Takes part in: vision — see every part of each lit together.
Where it is
There are two, one per eye. Each starts at the optic disc at the back of the eyeball, where the retina’s nerve fibres gather and leave the eye. [1][3]
It runs back and toward the midline through the orbit (eye socket), leaves it through the optic canal in the sphenoid bone, with the ophthalmic artery alongside it, and ends at the optic chiasm. [1][4]
Inside the skull its last stretch lies under the front of the brain, just in front of the hypothalamus and pituitary stalk, where the two nerves meet. [1][5]
What it does
It carries the visual signals from the retina to the brain: its fibres are the axons of the retina’s ganglion cells, the last nerve cells in the eye’s own circuit. [1][6]
Each nerve holds roughly a million such fibres (counts in adults range from about 770,000 to 1.7 million). [1]
It is the second of the twelve pairs of cranial nerves, but it is really part of the central nervous system: it grows out of the brain in the embryo, its fibres are insulated by oligodendrocytes like those of the brain, and it is wrapped in the same three meninges as the brain. [1][7]
Where the fibres leave the eye at the optic disc there are no light-sensing cells, which makes the blind spot each eye has; the other eye and the brain fill the gap in. [3][8]
Connections
From: the retina of its own eye. To: the optic chiasm, where the fibres from the nasal half of the retina cross to the other side and the rest continue on the same side into the optic tracts. [1][5]
Other names
Cranial nerve II (CN II), second cranial nerve; nervus opticus (Latin). [1]
Size
On this model the left optic nerve measures about 49 mm front to back, 22 mm top to bottom and 32 mm side to side (the box it fits in, not its volume); the right one is its mirror image. [2]
Centre of the left optic nerve compared with the centre of the optic chiasm: 20 mm further forward, 11 mm lower, 16 mm further from the midline; 28 mm apart in a straight line. [2]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.