optic chiasm


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chiasm

 [ki´azm]
a decussation or X-shaped crossing.
optic chiasm a structure in the forebrain formed by the decussation of fibers of the optic nerve from each half of each retina.

op·tic chi·asm

[TA]
a flattened quadrangular body in front of the tuber cinereum and infundibulum, the point of crossing or decussation of the axons of the optic nerves. Axons from the nasal retina cross to the opposite side, whereas axons from the temporal retina run directly caudal without crossing; some pass transversely on the posterior surface between the two optic tracts, and others pass transversely on the anterior surface between the two optic nerves.

op·tic chi·asm

(op'tik kī'azm) [TA]
A flattened quadrangular body in front of the tuber cinereum and infundibulum, the point of crossing or decussation of the fibers of the optic nerves; most of the fibers cross to the opposite side, some run directly forward on each side without crossing, some pass transversely on the posterior surface between the two optic tracts and others pass transversely on the anterior surface between the two optic nerves.
Synonym(s): optic decussation.

op·tic chi·asm

(op'tik kī'azm) [TA]
A flattened quadrangular body in front of the tuber cinereum and infundibulum, the point of crossing or decussation of the fibers of the optic nerves.
Synonym(s): optic decussation
References in periodicals archive ?
(b) Imaging one month later with T1-weighted MRI demonstrating a 22.0 x 12.0 mm bilobed mass with 8 mm suprasellar extension exerting mass effect on overlying optic chiasm.
Additionally and concurrent with rotatory visual pathway shift, there is depression of the optic chiasm relative to the diaphragma sella line.
Caption: Figure 2 The normal visual pathway showing the nasal optic nerve fibres crossing at the optic chiasm, projecting to the contralateral side of the visual cortex.
Sievers, "Optic nerve regeneration after intravitreal peripheral nerve implants: trajectories of axons regrowing through the optic chiasm into the optic tracts," Journal of Neurocytology, vol.
I then arrived at a 'stunning glimpse of the obvious': optometrists deal with conditions that go as far as the back of the eye; opthalmologists tend not to look beyond the optic chiasm; while occupational therapists deal with the whole spectrum, from the front of the eye to the back of the brain.
Twelve-year-old Poppy, from Tamworth, was diagnosed at 14 months old with Optic Chiasm Glioma, a brain tumour behind the eye, a condition which gave her a 50 per cent chance of survival.
To confirm the ruptured IDC, MRI (T1, T2, FLAIR and diffusion-weighted imaging-DWI-) was taken and mainly hypointense and laterally non-homogeneously iso-to hyperintense signal of dermoid cyst adherent to the optic chiasm, cavernous sinus and also spilling of fatty particles into the subarachnoid space were seen (Figure 1).
The differential diagnoses of intrasellar lesions include: adenoma, cyst of Rathke's pouch, craniopharyngioma, glioma of the optic chiasm or hypothalamus, meningioma, germ cell tumor, hamartoma, lipoma, dermoid or epidermoid cyst, metastasis; and granulomatous entities like lymphocytic hypophysitis, sarcoidosis, or Langerhans' histiocytosis [37].
The coalescence of multiple granulomas in the brain parenchyma can produce space-occupying lesions, most commonly in the optic chiasm, floor of the third ventricle, and pituitary stalk, but can occur anywhere in the CNS.
RADIOLOGIC DIAGNOSIS: Findings are consistent with persistent fetal vasculature syndrome (PFVS) of the right eye associated with microphthalmia, bilateral optic nerve and optic chiasm hypoplasia, and absence of the neurohypophysis.
Initial imaging revealed a space-occupying, non-enhancing lesion in the optic chiasm. An excision biopsy showed a grade II astrocytoma.