Optic nerve


The optic nerve, also known as cranial nerve II, is a continuation of the axons of the ganglion cells in the retina.

The optic nerve is a central tract of many axons of ganglion cells connecting primarily to the lateral geniculate body, a visual relay station in the diencephalon.

The optic nerve carries the ganglion cell axons to the brain, and the blood vessels that supply the retina.

An outward form of the diencephalon during embryogeneis.

The nerve is wrapped by the nerve sheat, which is derived from 3 layers of meninges and protrudes toward the orbit.

CSF moves freely between the intracranial and intraorbital subarachnoid spaces.

There are approximately 1.1 million nerve cells in each optic nerve.

A white-matter tract that relays information from the retina to the brain area of visual processing.

The optic nerve leaves the back of the eye to go to the optic chiasm, located just below and in front of the pituitary gland.

In the optic chiasm, the optic nerve fibers emanating from the nasal half of each retina cross over to the other side; but the nerve fibers originating in the temporal retina do not cross over.

The nerve fibers become the optic tract, passing through the thalamus and turning into the optic radiation until they reach the visual cortex in the occipital lobe at the back of the brain where the visual center of the brain is located.

The visual cortex ultimately interprets the electrical signals produced by light stimulation of the retina, via the optic nerve, as visual image.

The beginning of the optic nerve in the retina is called the optic nerve head or optic disc.

The optic disc cannot respond to light stimulation and is known as the blind spot.

Optic atrophy of the optic disc is the result of degeneration of the nerve fibers of the optic nerve and optic tract.

US of the optic nerve sheath diameter may be useful in determining and evaluation intracranial pressures.

Optic atrophy can be congenital or acquired.

Optic atrophy that is acquired can be due to vascular disturbances such as occlusions of the central retinal vein or artery or arteriosclerotic changes within the optic nerve itself, may be secondary to degenerative retinal disease such as optic neuritis or papilledema, may be a result of pressure against the optic nerve, or may be related to metabolic diseases such as diabetes), trauma, glaucoma, or toxicity to alcohol, tobacco, or other toxins.

Optic atrophy is associated with loss of vision .

A pale optic disc and loss of pupillary reaction are usually proportional to the visual loss.

Degeneration and atrophy of optic nerve fibers is irreversible, although in some cases, intravenous steroid injections have been seen to slow down the process.

Inflammation of the optic nerve is ref2242ed to as optic neuritis.

Optic neuritis may affect the part of the nerve and disc within the eyeball or the area behind the eyeball,retrobulbar optic neuritis, causing pain with eye movement.

Optic neuritis can be caused by demyelinating processes such as multiple sclerosis or post infectious encephalomyelitis, systemic infections of viral and bacterial disease, and metabolic diseases including pernicious anemia, diabetes and hyperthyroidism, inflammatory processes such as meningitis, chorioretinitis, tuberculosis, sinusitis, and syphilis, and toxins such as tobacco, quinine, salicylates, arsenic and lead. Papilledema is edema or swelling of the optic disc, most commonly due to an increase in intracranial pressure.

Papilledema usually is bilateral, the nerve head is very elevated and swollen, and pupil response typically is normal.

Secondary optic atrophy and permanent vision loss can occur if the primary cause of the papilledema is left untreated.

Ischemic optic neuropathy results from loss of the arterial blood supply to the optic nerve, as a result of occlusive disorders of the nutrient arteries.

Optic neuropathy is divided into anterior and posterior types.

Anterior optic neuropathy causes a pale edema of the optic disc,

Posterior optic neuropathy the optic disc is not swollen and the abnormality occurs between the eyeball and the optic chiasm.

Ischemic anterior optic neuropathy usually causes a loss of vision that may be sudden or occur over several days.

Ischemic posterior optic neuropathy is uncommon, and is related to stroke and brain tumors.

Glaucoma an insidious disease which damages the optic nerve, typically because the intraocular pressure is higher than the retinal ganglion cells can tolerate, leading to death of the ganglion cells and their axons comprising the optic nerve.

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