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A number of theories have been proposed for the function of the optic chiasm in vertebrates (see theories). According to the Axial Twist theory the optic chiasm develops as a consequence of a twist in the early embryo. [16] In Siamese cats with certain genotypes of the albino gene, the wiring is disrupted, with more of the nerve-crossing than ...
Chiasms are found in vertebrates but also in invertebrates. The optic chiasm in vertebrates can be of type I or II. [1] [4] However, an optic chiasm of type III is found in many insects [2] and in cephalopods. [3] In vertebrates, three of the cranial nerves show a chiasm. The optic chiasm of the optic tract (type I or II)
The optic tract is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus (LGN), pretectal nuclei, and superior colliculus. [14] The optic tract represents the first stage in the visual pathway in which visual information is transferred in a homonymous nature. [15]
The optic nerves from both eyes meet and cross at the optic chiasm, [33] [34] at the base of the hypothalamus of the brain. At this point, the information coming from both eyes is combined and then splits according to the visual field.
Once RGCs reach the chiasm, the glial cells supporting them will change from an intrafascicular to radial morphology. A group of diencephalic cells that express the cell surface antigen stage-specific embryonic antigen (SSEA)-1 and CD44 will form an inverted V-shape. [24] They will establish the posterior aspect of the optic chiasm border.
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.
Bitemporal hemianopsia is the medical description of a type of partial blindness where vision is missing in the outer half of both the right and left visual field. It is usually associated with lesions of the optic chiasm, the area where the optic nerves from the right and left eyes cross near the pituitary gland.
In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus. [1] [2]