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The optic chiasm, or optic chiasma is the part of the brain where both optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. [7] Signs and symptoms associated with optic chiasm lesions are also known as chiasmal syndrome.
The optic chiasm is found in all vertebrates, although in cyclostomes (lampreys and hagfishes), it is located within the brain. [2] [3] This article is about the optic chiasm of vertebrates, which is the best known nerve chiasm, but not every chiasm denotes a crossing of the body midline (e.g., in some invertebrates, see Chiasm (anatomy)).
Retinal ganglion cells (RGCs) from the inner halves of each retina (the nasal sides) decussate (cross to the other side of the brain) through the optic chiasma (khiasma means "cross-shaped"). RGCs from the outer half of each retina (the temporal sides) remain on the same side of the brain.
It is situated at the base of the brain, between the two cerebral peduncles of midbrain and dorsum sellae and continuous below with the pontine cistern and superiorly with the chiasmatic cistern. It contains: The optic chiasm; The bifurcation of the basilar artery; Peduncular segments of the posterior cerebral arteries (PCA)
Enlargement of the optic nerve along with a downward kink in the mid-orbit is usually observed. [5] While CT scans allow for optic nerve evaluation, MRI allows for intracranial evaluation to observe if the tumor has extended to other regions such as the optic chiasm and hypothalamus. [6]
MRI, CT scan Pilocytic astrocytoma (and its variant pilomyxoid astrocytoma ) is a brain tumor that occurs most commonly in children and young adults (in the first 20 years of life). They usually arise in the cerebellum , near the brainstem , in the hypothalamic region, or the optic chiasm , but they may occur in any area where astrocytes are ...
Clinically, no optic field deficits have been observed in a small series of optic nerve sections at the optic nerve-chiasm junction. [3] Several important structures are located adjacent to the optic chiasm. The supraclinoid branches of the internal carotid artery flank the chiasm. The cavernous sinuses are lateral and inferior to the chiasm.
If the part of the nerve between the eye and the chiasm is compressed, the result is vision loss in one eye. If the part after the chiasm is affected, visual loss on one side of the visual field occurs. [2] Adjacent to the pituitary lies a part of the skull base known as the cavernous sinus. This contains a number of nerves that control the eye ...