Nerve: Optic Nerve The left optic nerve and the optic tracts. Inferior view of the human brain, with the cranial nerves labelled. Latin nervus opticus Gray's subject #197 882 MeSH Optic+Nerve Cranial Nerves CN I – Olfactory CN II – Optic CN III – Oculomotor CN IV – Trochlear CN V – Trigeminal CN VI – Abducens CN VII – Facial CN VIII – Vestibulocochlear CN IX – Glossopharyngeal CN X – Vagus CN XI – Spinal Accessory CN XII – Hypoglossal
The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.
The optic nerve is the second of twelve paired cranial nerves but is considered to be part of the central nervous system, as it is derived from an outpouching of the diencephalon during embryonic development. As a consequence, the fibres are covered with myelin produced by oligodendrocytes, rather than Schwann cells, which are found in the peripheral nervous system, and are encased within the meninges. The name "optic nerve" is, in the technical sense, a misnomer, as the optic system lies within the central nervous system and therefore should be named the "optic tract," as nerves exist only, by definition, within the peripheral nervous system. Therefore, peripheral neuropathies like Guillain-Barré syndrome do not affect the optic nerve.
The optic nerve is ensheathed in all three meningeal layers (dura, arachnoid, and pia mater) rather than the epineurium, perineurium, and endoneurium found in peripheral nerves. Fibre tracks of the mammalian central nervous system (as opposed to the peripheral nervous system) are incapable of regeneration, and, hence, optic nerve damage produces irreversible blindness. The fibres from the retina run along the optic nerve to nine primary visual nuclei in the brain, whence a major relay inputs into the primary visual cortex.
The optic nerve is composed of retinal ganglion cell axons and support cells. It leaves the orbit (eye socket) via the optic canal, running postero-medially towards the optic chiasm, where there is a partial decussation (crossing) of fibres from the nasal visual fields of both eyes. Most of the axons of the optic nerve terminate in the lateral geniculate nucleus from where information is relayed to the visual cortex, while other axons terminate in the pretectal nucleus and are involved in reflexive eye movements. Other axons terminate in the suprachiasmatic nucleus and are involved in regulating the sleep-wake cycle. Its diameter increases from about 1.6 mm within the eye to 3.5 mm in the orbit to 4.5 mm within the cranial space. The optic nerve component lengths are 1 mm in the globe, 24 mm in the orbit, 9 mm in the optic canal, and 16 mm in the cranial space before joining the optic chiasm. There, partial decussation occurs, and about 53% of the fibers cross to form the optic tracts. Most of these fibres terminate in the lateral geniculate body.
From the lateral geniculate body, fibers of the optic radiation pass to the visual cortex in the occipital lobe of the brain. In more specific terms, fibers carrying information from the contralateral superior visual field traverse Meyer's loop to terminate in the lingual gyrus below the calcarine fissure in the occipital lobe, and fibers carrying information from the contralateral inferior visual field terminate more superiorly.
Each optic nerve contains around 1.2 million nerve fibers, which are axons of the retinal ganglion cells of one retina. In the fovea, which has high acuity, these ganglion cells connect to as few as 5 photoreceptor cells; in other areas of retina, they connect to many thousand photoreceptors.
Role in disease
Damage to the optic nerve typically causes permanent and potentially severe loss of vision, as well as an abnormal pupillary reflex, which is diagnostically important. The type of visual field loss will depend on which portions of the optic nerve were damaged. In general:
- Damage proximal to the optic chiasm causes loss of vision in the visual field of the same side only.
- Damage in the chiasm causes loss of vision laterally in both visual fields (bitemporal hemianopia). It may occur in large pituitary adenomata.
- Damage distal to the chiasm causes loss of vision in one eye but affecting both visual fields: The visual field affected is located on the opposite side of the lesion.
Injury to the optic nerve can be the result of congenital or inheritable problems like Leber's Hereditary Optic Neuropathy, glaucoma, trauma, toxicity, inflammation, ischemia, infection (very rarely), or compression from tumors or aneurysms. By far, the three most common injuries to the optic nerve are from glaucoma, optic neuritis (especially in those younger than 50 years of age), and anterior ischemic optic neuropathy (usually in those older than 50).
Anterior Ischemic Optic Neuropathy is a particular type of infarct that affects patients with an anatomical predisposition and cardiovascular risk factors.
Optic nerve hypoplasia is the under-development of the optic nerve causing little to no vision in the affected eye.
Ophthalmologists, in particular, those sub-specialists that are neuro-ophthalmologists, are often best suited to diagnose and treat diseases of the optic nerve.
The International Foundation for Optic Nerve Diseases IFOND sponsors research and information on a variety of optic nerve disorders and may provide general direction.
The ophthalmic artery and its branches. (optic nerve is yellow)
The fornix and corpus callosum from below.
- online case history - Optic nerve analysis with both scanning laser polarimetry with variable corneal compensation (GDx VCC) and confocal scanning laser ophthalmoscopy (HRT II - Heidelberg Retina Tomograph). Also includes actual fundus photos.
- lesson3 at The Anatomy Lesson by Wesley Norman (Georgetown University) (orbit4)
- cranialnerves at The Anatomy Lesson by Wesley Norman (Georgetown University) (II)
- Notes on Optic Nerve
Nerves of head and neck: the cranial nerves and nuclei (TA A14.2.01, GA 9.855) olfactory (AON->I) optic (LGN->II) oculomotor
trochlear (TN->IV)no significant branches trigeminal
(PSN, TSN, MN, TMN->V)
abducens (AN->VI)no significant branches facial (FMN, SN, SSN->VII)near origininside
(NA, ISN, SN->IX)before jugular fossaafter jugular fossa
(NA, DNVN, SN->X)before jugular fossaafter jugular fossa
accessory (NA, SAN->XI) hypoglossal (HN->XII) Sensory system: Visual system and eye movement pathways Visual perception Muscles of orbitTrackingHorizontal gazeVertical gaze Pupillary reflexPupillary dilation Circadian rhythm
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Optic Nerve — may refer to: Optic nerve, the anatomical structure Optic Nerve (comic), the comic book series Optic Nerve (1999), a Red Hot Benefit Series tribute to David Wojnarowicz This disambiguation page lists articles associated with the same title. If an … Wikipedia
optic nerve — n. either of the second pair of cranial nerves, which connect the retina of the eye with the brain: see EYE … English World dictionary
Optic nerve — The optic nerve connects the eye to the brain. The optic nerve carries the impulses formed by the retina, the nerve layer that lines the back of the eye and senses light and creates impulses. These impulses are dispatched through the optic nerve… … Medical dictionary
optic nerve — Anat. either one of the second pair of cranial nerves, consisting of sensory fibers that conduct impulses from the retina to the brain. See illus. under eye. [1605 15] * * * ▪ anatomy second cranial nerve, which carries sensory nerve impulses… … Universalium
optic nerve — UK / US noun [countable] Word forms optic nerve : singular optic nerve plural optic nerves medical the large nerve that sends signals relating to sight from the retina in your eye to your brain … English dictionary
optic nerve — each optic nerve emerges from the anterior ventral corner of each optic lobe. The nerves cross over beneath the telencephalon … Dictionary of ichthyology
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optic nerve — regos nervas statusas T sritis fizika atitikmenys: angl. optic nerve vok. Sehnerv, n rus. зрительный нерв, m pranc. nerf optique, m … Fizikos terminų žodynas