Optic Nerve

Nervus opticus

For medical students2 min readUpdated 2026-10-10

The optic nerve is the second cranial nerve (CN II), classified as a special somatic afferent (SSA) nerve. It is formed by the bundles of axons from retinal multipolar neurons and is responsible for transmitting visual impulses from the eye to the visual processing centers of the brain.

Nerve typeSpecial sensory (no motor fibers)

OriginAxons of retinal multipolar neurons (ganglion cells)

EndpointPrimary visual cortex in the occipital lobe

Topography and Parts of the Optic Nerve

Along its course from the eyeball to the intracranial structures, the optic nerve (nervus opticus) is conventionally divided into several topographical segments:

Orbital (intraorbital) part (pars orbitalis / pars intraorbitalis) — the segment located directly within the orbital cavity.
Canalicular (intraosseous) part (pars intracanalicularis) — the fragment passing through the bony optic canal.
Intracranial part (pars intracranialis) — the terminal segment of the nerve entering the cranial cavity up to the formation of the optic chiasm.

Optic Chiasm (Chiasma opticum)

Upon reaching the region of the sella turcica, the fibers of the right and left optic nerves undergo a partial decussation. This anatomical structure is called the optic chiasm (chiasma opticum).

Specific groups of axons behave differently:

Medial (nasal) fibers of each nerve cross over to the contralateral side.
Lateral (temporal) fibers continue on their ipsilateral side (uncrossed).

Optic Tracts and Cortical Pathway

Immediately after the chiasma opticum, the optic tracts (tractus optici) are formed. Due to the preceding partial decussation, each optic tract contains combined information: axons from the temporal half of the ipsilateral retina and axons from the nasal half of the contralateral retina.

The further central visual pathway proceeds as follows:

The optic tracts sweep around the cerebral peduncles.
The fibers reach the subcortical visual centers and synapse.
From the subcortical structures, the next stage begins: the nerve bundles pass through the posterior limb of the internal capsule.
They form the optic radiation (radiatio optica).
The pathway terminates in the primary visual cortex of the occipital lobe.

Mnemonic

To remember retinal decussation: "Medial fibers cross the line, lateral fibers stay in line." Medial fibers switch to the contralateral half, while lateral fibers proceed uncrossed.

Frequently asked questions

What topographical parts is the optic nerve divided into along its course?

The optic nerve is divided into four topographical parts:

intraorbital part — pars intraorbitalis n. optici;
orbital part — pars orbitalis;
canalicular part — pars intracanalicularis;
intracranial part — pars intracranialis.

What anatomical structures serve as the subcortical visual centers where the optic tracts terminate?

The subcortical visual centers include:

lateral geniculate body — corpus geniculatum laterale, where the majority of optic tract axons terminate;
superior colliculi — colliculi superiores, which receive a smaller portion of visual fibers.

In which sulcus of the occipital lobe is the primary visual cortex located?

The primary visual cortex is located along the banks of the calcarine sulcus — sulcus calcarinus — in the occipital lobe.

What structures pass through the optic canal along with the optic nerve?

Blood vessels pass through the optic canal alongside the optic nerve.

Ophthalmic artery (a. ophthalmica) — a major branch of the internal carotid artery, located lateral to the optic nerve.
Central retinal artery (a. centralis retinae) — a branch of the ophthalmic artery that enters the optic nerve directly to supply the inner layers of the retina.

Does the optic nerve contain motor fibers?

No, the optic nerve (CN II) is exclusively a special sensory nerve. It contains no motor fibers.

Where does the decussation of the optic nerves occur?

The partial decussation of fibers (chiasma opticum) occurs within the cranial cavity, directly in the region of the sella turcica.

Which fibers make up the right optic tract?

The right optic tract collects fibers from the right (temporal) half of the right eye's retina and the left (nasal) half of the left eye's retina.

Where does the central visual pathway end?

After passing through the internal capsule and forming the optic radiation, the pathway terminates in the visual cortex of the occipital lobe.

Go deeper

Detailed topography of the orbital part (pars orbitalis) of the optic nerve.
Anatomical relationships of the canalicular part (pars intracanalicularis) within the optic canal.
Topography of the optic chiasm (chiasma opticum) relative to the sella turcica.
Structure of subcortical visual centers and their connections.
Course of the optic radiation (radiatio optica) through the posterior limb of the internal capsule.