Optic Chiasm: What Is It And What Are Its Functions?

Vision is one of the most developed and important senses for human beings. In fact we have a brain 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 said 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.

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. It is a small X-shaped structure located in the anterior cerebral fossa, somewhat 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.

Something of capital importance happens in the optic chiasm so that we can correctly capture visual information: in this structure, a decussation of about half of the fibers of the optic nerve 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 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 visual field. Thus, the nerve fibers that carry information from the left side of the retina of the right eye come together 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.

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 it did not occur (or a decussation of all the fibers occurred), the information received by each eye would be processed by only 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 the brain can later integrate the information and capture elements such as the depth or distance at which the observed element is. .

Consequences of your injury

Craniocerebral trauma, surgeries or strokes, along with some diseases and disorders such as tumors, can 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, this injury can cause a great impact on our visual system The most common cause is usually 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 condition involves the inability to see half of the visual field, even though the eyes function perfectly. It can be bitemporal (if it is the fibers that decussate that are damaged) or binasal (if it is the fibers 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 cause serious consequences such as loss of vision or in some cases diencephalic syndrome.

Some injuries produced at the moment when 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 as the injury. as well as a possible contralateral problem if there is damage to the decussating fibers.