optic nerve

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optic

 [op´tik]
ocular (def. 1).
optic nerve the second cranial nerve; it is purely sensory and is concerned with carrying impulses for the sense of sight (see vision). See anatomic Table of Nerves in the Appendices.

The rods and cones of the retina are connected with the optic nerve which leaves the eye slightly to the nasal side of the center of the retina. The point at which the optic nerve leaves the eye is called the blind spot because there are no rods and cones in this area. The optic nerve passes through the optic foramen of the skull and into the cranial cavity. It then passes backward and undergoes a division; those nerve fibers leading from the nasal side of the retina cross to the opposite side while those from the temporal side continue to the thalamus uncrossed. After synapsing in the thalamus the neurons convey visual impulses to the occipital lobe of the brain.

Degenerative and inflammatory lesions of the optic nerve occur as a result of infections, toxic damage to the nerve, metabolic or nutritional disorders, or trauma. Syphilis is the most frequent cause of infectious disorders of the optic nerve. Methanol (methyl alcohol) is highly toxic to the optic nerve and can cause total blindness. Diabetes mellitus and anemia are examples of metabolic and nutritional disorders that can lead to damage to the optic nerve and produce serious loss of vision.

Treatment of optic neuritis is aimed at control of the primary cause of the disorder. Cortisone and similar steroids are often used to relieve symptoms; however, nothing can be done to regain sight lost through damage to the nerve.

optic nerve

n.
Either of the second pair of cranial nerves that arise from the retina and carry visual information to the thalamus and other parts of the brain.

optic nerve

one of a pair of nerves that transmit visual impulses. The optic nerve is not a true cranial nerve but is rather an extension of the brain. It consists mainly of coarse myelinated fibers that arise in the retinal ganglionic layer, traverse the thalamus, and connect with the visual cortex. At the optic chiasm the fibers from the inner or nasal half of the retina cross to the optic tract of the opposite side. The remaining fibers from the temporal or outer half of each retina are uncrossed and pass to the visual cortex on the same side. The visual cortex functions in the perception of light, shade, and objects. The optic nerve fibers correspond to a tract of fibers within the brain. Also called nervus opticus, second cranial nerve.
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Optic nerve

optic nerve

2nd cranial nerve Anatomy A bundle of > 1 million nerve fibers that carries afferent/senosry fibers from the retinal gangliion cells, passing out of the orbit via the optic foramen (canal) to the optic chiasm, where part of the fibers cross to the opposite side, passing though the optic tract to the geniculate bodys, pretectum, and superior colliculus in the brain

Optic nerve

A bundle of nerve fibers that carries visual messages from the retina in the form of electrical signals to the brain.

optic

of or pertaining to the eye.

optic chiasma
see optic chiasm.
optic cortex
see visual cortex.
optic cup activity
optic disk
the disk in the fundus of the eye marking the point at which the optic nerve enters; it is accompanied by blood vessels, is oval, light in color and the blind spot of the retina.
optic nerve
the second cranial nerve; it is purely sensory and is concerned with carrying impulses for the sense of sight. The rods and cones of the retina are connected with the optic nerve which leaves the eye slightly to the nasal side of the center of the retina. The point at which the optic nerve leaves the eye is called the blind spot because there are no rods and cones in this area. The optic nerve passes through the optic foramen of the skull and into the cranial cavity. It then passes backward and undergoes a division; those nerve fibers leading from the nasal side of the retina cross to the opposite side in the optic chiasma while those from the temporal side continue to the thalamus uncrossed. The nerve tracts proceeding backward from the optic chiasm, pass around the cerebral peduncle, and dividing into a lateral and medial root, which end in the superior colliculus and lateral geniculate body, respectively. After synapsing in the thalamus the neurons convey visual impulses to the occipital lobe of the brain.
Injury to the nerve leads to partial or complete loss of sight on the opposite side. Commonly bilateral.
optic nerve aplasia
an uncommon congenital anomaly, most frequently seen in Collie dogs; affected animals are blind from birth. Hypovitaminosis A and prenatal infection with bovine virus diarrhea are possible causes.
optic nerve inflammation
optic neuritis.
optic primordia
the eyes begin in the embryo as a pair of shallow optic grooves on each side of the developing forebrain. The grooves form optic vesicles which invaginate to form a double-walled optic cup.
optic radiation
fibers from the lateral geniculate body entering the occipital cortex.
optic stalk
the evagination from the neural tube of the developing embryo which develops the optic cup at its extremity; the stalk persists as the optic nerve.
optic sulcus
see optic groove.
optic vesicle
the initial evagination from the neural tube which gives rise to the optic cup and the optic stalk.