Optic chiasm: what is it and what are its functions?

Vision is one of the most developed and important senses for humans. In fact, we have a cerebral lobe, the occipital, which has been especially linked to aspects related to the vision and the processing and integration of the information coming from this sense.

But the visual information does not appear in said lobe just like that. First, the information coming from each eye must be captured, integrated and later analyzed and processed. There are several points of great interest in the visual system, one of them being optic chiasm. It is about this structure that we are going to talk about in this article.

• Related article: "Parts of the human brain (and functions)"

The optic chiasm: what is it and where is it located?

The optic chiasm is a part of the brain that is of great importance when it comes to being able to process visual information coming from the retina, being the point where the optic nerves of both eyes meet. It is a small X-shaped structure (X) located in the anterior cerebral fossa, somewhat above and below 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

Something of paramount importance happens in the optic chiasm so that we can correctly capture visual information: in this structure, a decussation of about half of the optic nerve fibers. And it is that the optic nerve divides into two tracts when it reaches the optic chiasm, one nasal and the other temporal. Nasal fibers from each eye cross to the other Cerebral hemisphere, while the temporal ones continue through the same hemisphere, until they reach the lateral geniculate nucleus of the thalamus.

In addition to this, it is relevant to take into account that the nerve fibers of each eye that end up joining in the optic chiasm have a special relationship: these are the fibers that receive information from a specific side of the field visual. 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. of 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 left eye. right.

• You may be interested in: "The 11 parts of the eye and their functions"

Function

The optic chiasm, by allowing and facilitating the decussation of part of the optic fibers, allows both cerebral hemispheres to receive visual information from both eyes: if no decussation occurred (or a decussation of all fibers occurred), the information received by each eye would only be processed by one of them, there being no good integration of the material.

In this way, the images captured by each eye can be processed and contrasted, resulting in great importance when it comes to later the brain can integrate the information and capture elements such as the depth or the distance at which the observed element is.

• You may be interested in: "Visual agnosia: the inability to understand visual stimuli"

Consequences of your injury

Head injuries, surgeries or strokes, along with some diseases and alterations such as tumors, may be the reason that the optic chiasm or the nerve pathways that circulate through it they get injured Although it is not frequent, given its position inside the skull, said lesion can cause a great affectation in our visual system. The most common cause is usually compression, although fiber breakage can also occur.

Specifically, cases of partial blindness or hemianopia caused by alterations in the optic chiasm have been observed. This affectation means the inability to see one half of the visual field, despite the fact that the eyes work perfectly. It can be bitemporal (if the fibers that decussate are damaged) or binasal (if the fibers that do not decussate are damaged).

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 cause serious consequences such as loss of vision or in some cases diencephalic syndrome.

Some lesions produced when the optic nerve enters the optic chiasm can generate a junctional scotoma, causing visual deficits within a visual field, usually in the central area on the same side of the body as the lesion, as well as a possible contralateral problem if there is damage to the fibers that decuss

Bibliographic references

• 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.; Avendano-Mendez-Padilla, J.; Garcia-Gonzalez, U.; Romero-Vargas, S. (2014). The optic chiasm and its exciting study through twenty centuries. Archives of the Spanish Society of Ophthalmology, 89 (10).