Optical chiasm: what is it and what are its functions?
Vision is one of the most developed and important senses for the human being. In fact we have a cerebral lobe, the occipital, which has been linked especially to aspects related to vision and processing and integration of information from this sense.
But visual information does not appear in that lobe just like that. First, the information from each eye must be captured, integrated and subsequently analyzed and processed. There are several points of great interest in the visual system, one of them being the optic chiasm . It is about this structure that we are going to talk about in this article.
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The optic chiasm: what is it and where is it?
The optical chiasm is a part of the brain that is of great importance when it comes to processing visual information from the retina, being the point at which the optic nerves of both eyes meet. It is a small structure in the form of X (X) located in the anterior cerebral fossa, something above and in front of the diaphragm of the sella turcica (small niche in the sphenoid bone that houses the pituitary gland) and in front of the hypothalamus.
In the optical chiasm something of capital importance happens so that we can correctly capture the visual information: in this structure it is produced a decussation of about half of the fibers of the optic nerve . And is that the optic nerve is divided into two tracts to reach the optic chiasm, one nasal and one temporary. The nasal fibers from each eye cross to the other cerebral hemisphere, while the temporal fibers continue through the same hemisphere, until they reach the lateral geniculate nucleus of the thalamus.
In addition, it is important to bear in mind that the nerve fibers of each eye that end up coming together in the optic chiasm have a special relationship: they are the fibers that receive information from a specific side of the visual field. Thus, the nerve fibers that carry information from the left side of the retina of the right eye join with those that carry the same information from the left eye, while the fibers that carry information from the right side of the retina of the left eye do the same with those of the right.
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The optical chiasm, by allowing and facilitating the decussation of part of the optical fibers, allows both cerebral hemispheres to receive visual information from both eyes : if it did not occur (or a decussation of all fibers occurred), the information received by each eye would be processed only by one of them, and there is no good integration of the material.
It is allowed in this way that the images that each eye captures can be processed and contrasted, being of great importance at the time that the brain can later integrate the information and capture elements such as depth or distance to which the observed element is .
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Consequences of your injury
Cranioencephalic injuries, surgeries or cerebrovascular accidents, along with some diseases and disorders such as tumors, can cause the optic chiasm or nerve pathways that circulate through it to be injured. Although it is not frequent, given its position inside the skull, said injury can cause a great impact on our visual system . The most common cause is compression, although fiber breakage can also occur.
Specifically, cases of partial blindness or hemianopsia caused by alterations in the optic chiasm have been observed. This affectation supposes the incapacity to see a half of the visual field, in spite of which the eyes work perfectly. It can be bitemporal (if they are the fibers that decuss those that are damaged) or binasal (if they are those that do not decussate).
Another possible alteration is the appearance of an optic glioma , which can appear both within the optic chiasm itself and together with tumors in the hypothalamus. The glioma in question is usually a benign tumor, although it can generate serious consequences such as loss of vision or in some cases diencephalic syndrome.
Some lesions produced at the moment in which the optic nerve penetrates the optic chiasm can generate a scotoma of the junction, causing visual deficits within a visual field, generally in the central area of the same side of the body in which the lesion is located, as well as a possible contralateral problem if there is damage to the fibers that decussate.
- Adel K. Afifi. (2006). Functional neuroanatomy: Text and atlas.Mexico D.F .: McGraw Hill p.324
- Kandel, E.R .; Schwartz, J.H. & Jessell, T.M. (2001). Principles of neuroscience. Fourth edition. McGraw-Hill Interamericana. Madrid.
- Correa-Correa, V .; Avendaño-Méndez-Padilla, J .; García-González, U .; Romero-Vargas, S. (2014). The optical chiasma and its exciting study through twenty centuries. Archives of the Spanish Society of Ophthalmology, 89 (10).