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

This part of the brain plays a very important role in the processing of visual information.

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

But visual information does not appear in this lobe just like that. First the information coming from each eye must be captured, integrated and then 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 in this article.

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 processing visual information coming from the retina, being the point where the optic nerves of both eyes meet. information coming from the retina, being the point where the optic nerves of both eyes meet. It is a small X-shaped structure located in the anterior cerebral fossa, somewhat above and in front of the sella turcica diaphragm (small niche in the sphenoid bone that houses the pituitary gland) and in front of the hypothalamus.

In the optic chiasm something of capital importance happens so that we can correctly capture the visual information: in this structure takes place about half of the fibers of the optic nerve are decussated in this structure.. The optic nerve divides into two tracts when it reaches the optic chiasm, one nasal and the other temporal. The nasal fibers coming 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 note that the nerve fibers from each eye that end up joining 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 eye.

Function

The optic chiasm, by allowing and facilitating the decussation of part of the optic fibers, allows both cerebral hemispheres to receive the visual information coming from both eyes.If this did not occur (or if there was a decussation of all the fibers), the information received by each eye would be processed only by one of them, not having a good integration of the material.

This allows the images captured by each eye to be processed and contrasted, which is of great importance for the brain to later integrate the information and capture elements such as depth or the distance to the observed element.

Consequences of its lesion

Cranioencephalic trauma, surgeries or cerebrovascular accidents, together with some diseases and alterations such as tumors, may cause the optic chiasm or the nerve pathways that circulate through it to be injured. Although it is not frequent, given its position within the skull, such an injury may can cause a great affectation in our visual system.. The most common cause is usually compression, although fiber rupture can also occur.

Specifically, cases of partial blindness or hemianopsia caused by alterations in the optic chiasm have been observed. This condition involves the inability to see one half of the visual field, even though the eyes function perfectly. It may be bitemporal (if the decussating fibers are damaged) or binasal (if the non-decussing fibers are damaged).

Another possible alteration is the appearance of an optic glioma.The glioma in question is usually a benign tumor, although it can have serious consequences such as loss of vision or in some cases diencephalic syndrome. The glioma in question is usually a benign tumor, although it can have serious consequences such as loss of vision or in some cases diencephalic syndrome.

Some lesions produced at the moment when the optic nerve penetrates the optic chiasm can generate a junctional scotoma, causing visual deficits within a visual field, generally in the central area of the same side of the body where the lesion is located, as well as a possible contralateral problem if there is damage to the decussating fibers.

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.; Avendaño-Méndez-Padilla, J.; García-González, U.; Romero-Vargas, S. (2014). The optic chiasm and its exciting study through twenty centuries. Archivos de la Sociedad Española de Oftalmología, 89 (10).