Each eyeball sits in the front of its eye socket (orbit), a cone of seven skull bones directly under the front of the frontal lobe. It is about 24 mm across, and the optic nerve leaves its back, slightly toward the nose, to run back to the optic chiasm under the brain. [1][2][3]
The 3D brain needs JavaScript. The text below still says where the eyeball is and what it does.
Opens cut by a side (sagittal) slice through the eyeball. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
This model draws each eyeball as its sclera, the white outer coat that makes up most of its wall; the clear cornea at the front and the iris, lens and retina inside are not separate shapes here. [4]
Lit with it: the two optic nerves, in their own colour, so you can see where each leaves the back of its eye and runs to the optic chiasm. [4][5]
The eyeball fills the front of the orbit, the bony socket built from seven bones (frontal, sphenoid, zygomatic, maxilla, ethmoid, lacrimal and palatine). The orbit holds about 30 ml, of which the eye takes about 6.5 ml; fat, the eye muscles, nerves and vessels fill the rest. [2]
The roof of the orbit is the thin floor of the front of the skull, so each eye lies just under the frontal lobe: the orbitofrontal cortex is named for sitting immediately above the orbits. [2][6]
The optic nerve leaves the back of the eye at the optic disc, which lies 3 to 4 mm toward the nose from the fovea, the centre of sharp vision. [3]
What it does
It is a hollow ball with three layers: an outer fibrous layer (the white sclera and the clear cornea), a middle vascular layer (the choroid, ciliary body and iris) and an inner layer, the retina, which holds the light-sensing cells. [7]
The sclera makes up five sixths of the eye’s surface, most of it hidden inside the orbit; it keeps the eye’s shape and gives the six eye muscles something to pull on. [7][8]
Light is focused by the cornea, which gives about two thirds of the eye’s focusing power, and then by the lens, which the ciliary muscle thickens to focus on near things. [9][7]
The retina’s rods work in dim light and its cones give colour and fine detail; the cones are packed most densely in the fovea. Their signals leave the eye along the axons of the retina’s ganglion cells, which form the optic nerve. [7][10]
The retina grows out of the brain in the embryo, from the diencephalon, so it counts as part of the central nervous system. [10]
Connections
Out: the optic nerve, from the optic disc back to the optic chiasm. Moved by: six extraocular muscles attached to the sclera, worked by the oculomotor, trochlear and abducens nerves. [5][11]
Blood: the ophthalmic artery, the first branch of the internal carotid artery after it leaves the cavernous sinus, supplies the eye and the rest of the orbit. [12]
Other names
Eye, globe of the eye; bulbus oculi (Latin). The white of the eye is the sclera. [1][8]
Size
On this model the left eyeball measures about 25 mm front to back, 26 mm top to bottom and 26 mm side to side (the box it fits in, not its volume); the right one is its mirror image. [4]
Centre of the left eyeball compared with the centre of the optic chiasm: 46 mm further forward, 22 mm lower, 30 mm further from the midline; 59 mm apart in a straight line. [4]
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.