optic chiasma


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Related to optic chiasma: corpus callosum, optic tract

optic chiasma

n.
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 chiasma

The 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 chiasma

a 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.

chiasma, optic 

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.
Fig. C9 An illustration of the decussation of the optic nerve fibres occurring in the optic chiasmaenlarge picture
Fig. C9 An illustration of the decussation of the optic nerve fibres occurring in the optic chiasma
References in periodicals archive ?
Optic chiasma: Partial decussation of human retinal axons takes place in optic chiasma.
Retinotopic distribution of axons continues in optic chiasma
In the optic tract fibres from optic chiasma are rearranged to correspond with the position of lateral geniculate body.
Similarly, optic nerve or optic chiasma damage may cause visual blurring or diplopia.23
It may be accompanied by ventricular collapse and may include: Descent of Cerebellar tonsils, which maybe mistaken for an Arnold-Chiari malformation Type I, prepontine cistern effacement, an inferiorly displaced optic chiasma, obliteration or effacement of the prechaismatic cistern, and reduction of the subarachnoid cisterna.
In their case optic globe, nerves and optic chiasma was absent.
The re-calculation of the radiotherapy doses applied; showed that the tissues in the base of the skull, the brain and the optic chiasma would tolerate a maximum dose of further 45 Gy.