The optic tract is the flat band of visual fibres that runs from the back of the optic chiasm, around the side of the midbrain, to the lateral geniculate body under the back of the thalamus; there is one on each side. Each tract carries the opposite half of the visual field from both eyes. [1]
The 3D brain needs JavaScript. The text below still says where the optic tract is and what it does.
Slice
Opens cut by a top (axial) slice through the optic tract. 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
It continues the optic nerve fibres back from the optic chiasm on each side, on the underside of the brain beside the hypothalamus. [1]
From there it curves back and outward around the cerebral peduncle, the front of the midbrain, to reach the lateral geniculate body on the underside of the back of the thalamus. [1][2]
What it does
The left tract carries the right half of the visual field from both eyes and the right tract the left half: fibres from the temporal retina of the same-side eye and from the nasal retina of the other eye, which crossed in the chiasm. [1][3]
Most of its fibres end in the lateral geniculate body, the relay that passes vision on to the primary visual cortex. [1][2]
Smaller branches go to the pretectal area of the midbrain, which controls the pupil’s response to light, and to the superior colliculus, which turns the eyes toward what appears in view. [1][4][5]
Connections
From: the optic chiasm. To: the lateral geniculate body, the pretectal nuclei and the superior colliculus on its own side. [1]
After the lateral geniculate body the pathway carries on as the optic radiation to the primary visual cortex in the occipital lobe. [2][3]
Other names
Tractus opticus (Latin); the optic tracts (the pair). [1]
Size
On this model the left optic tract measures about 38 mm front to back, 8 mm top to bottom and 25 mm side to side (the box it fits in, not its volume); the right one is its mirror image. [6]
Centre of the left optic tract compared with the centre of the left lateral geniculate body: 11 mm further forward, 6 mm closer to the midline; 13 mm apart in a straight line. [6]
Centre of the left optic tract compared with the centre of the optic chiasm: 18 mm further back, 16 mm further from the midline; 24 mm apart in a straight line. [6]
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.