Sehnervs

Sehnervs refers to the optic nerve, the bundle of retinal ganglion cell axons that transmits visual information from the eye to the brain. There are two optic nerves, and they are considered part of the central nervous system.

Anatomy: Each optic nerve begins at the optic disc in the retina, traverses the orbit as the intraorbital segment, passes through the optic canal, and reaches the optic chiasm where nasal fibers cross to the contralateral side. Post-chiasm, fibers continue as the optic tracts to the lateral geniculate nucleus of the thalamus, which relays information to the visual cortex. The retina segment is unmyelinated; the nerve becomes myelinated posterior to the lamina cribrosa.

Blood supply and coverings: The optic nerve is surrounded by the meningeal coverings and receives arterial supply mainly from the ophthalmic artery via pial branches; the intraorbital portion also receives short posterior ciliary arteries. Venous drainage occurs through the central retinal vein and superior/inferior ophthalmic veins.

Clinical relevance: Lesions of the optic nerve produce visual field defects and a relative afferent pupillary defect. Common conditions include optic neuritis, ischemic optic neuropathy, glaucoma, and papilledema. Assessment includes fundoscopy, visual field testing, optical coherence tomography, and MRI if structural disease is suspected.

Development and significance: The optic nerve originates as an outgrowth of the diencephalon and is considered part of the central nervous system, with myelination by oligodendrocytes. The term Sehnervs is used in various languages to refer to this structure.