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A structure in the brain formed by the partial intersection or crossing of the optic nerve fibers on the underside of the hypothalamus. Also called optic chiasm.
optic chiasmaThe junction of the two OPTIC NERVES lying under the brain. In the chiasma optic nerve fibres from the inner half of each RETINA cross over. Those from the outer half do not. Thus fibres from the inner half of each retina run out of the chiasma in close association with fibres from the outer half of the retina on the other side. The two optic tracts so formed run into the brain. This arrangement ensures that input to both eyes from the right field of vision causes signals that pass to the left half of the brain, and vice versa.
optic chiasmaa point under the hypothalamus of the brain where the two optic nerves meet and cross over, so that stimuli from each eye are interpreted in the OPTIC LOBE of the opposite side of the brain.
A structure located above the pituitary gland and formed by the junction and partial decussation (crossing-over) of the optic nerves. The fibres from the nasal half of the retina of the left eye cross over to join the fibres from the temporal half of the right retina to make up the right optic tract and vice versa. About 53% of the axons of the optic nerves cross to the opposite tract (Fig. C9). A lesion of the chiasma produces a typical field defect (heteronymous hemianopia). Note: also spelt chiasm. See circle of Willis; decussation; visual pathway; stereo-blindness; optic tracts.
of or pertaining to the eye.
see optic chiasm.
see visual cortex.
optic cup activity
see intraretinal space.
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.
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
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.
fibers from the lateral geniculate body entering the occipital cortex.
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.
see optic groove.
the initial evagination from the neural tube which gives rise to the optic cup and the optic stalk.