What Is the Optic Chiasma?

Optic cross (optic chiasm), a section of the optic nerve. This segment is located on the saddle. Therefore, when there are lesions in the saddle region, multiple waves and optic cross can produce different degrees of visual field defects and visual impairment. It is a structure formed by the bilateral optic nerve fibers crossing at the midline. The fibers from the retinal temporal halves of the two eyes do not cross, and each enters the optic tract on different sides; the fibers from the nasal retinal halves cross, entering the contralateral visual tract. Optic intersection is generally located above the sphenoidal saddle, after the nodular nodule, anteriorly above the pituitary. If the visual intersection is located before the saddle tubercle, it is called anterior visual intersection; when the visual intersection is moved closer to the back of the saddle, it is called posterior visual intersection.

Optic cross (optic chiasm), a section of the optic nerve. This segment is located on the saddle. Therefore, when there are lesions in the saddle region, multiple waves and optic cross can produce different degrees of visual field defects and visual impairment. It is a structure formed by the bilateral optic nerve fibers crossing at the midline. The fibers from the retinal temporal halves of the two eyes do not cross, and each enters the optic tract on different sides; the fibers from the nasal retinal halves cross, entering the contralateral visual tract. Optic intersection is generally located above the sphenoidal saddle, after the nodular nodule, anteriorly above the pituitary. If the visual intersection is located before the saddle tubercle, it is called anterior visual intersection; when the visual intersection is moved closer to the back of the saddle, it is called posterior visual intersection.

Chinese name

Optic cross

Foreign name

optic chiasm

Distribution

More common in clinical

The main symptoms

For vision loss, visual impairment

Optic cross anatomy

Optic intersection: Optic intersection belongs to the hypothalamus, which is located on the underside of the brain. It is connected to the end plate above and below, gray nodules at the rear, and anterior penetrating mass on both sides. The part of the optic cross that extends forward and outward is called the optic nerve, which is connected to the eyeball; the fiber bundle that extends outward and backward is called the optic bundle. That is, the optic cross is composed of fibers inside the skull of the left and right optic nerves. When the fibers in the optic nerve reach the optic cross, the fibers of the nasal (medial) half of the left and right optic nerves cross, and the temporal (lateral) half The fibers of the part do not cross, and extend to form a visual bundle after crossing. Therefore, the lateral optic tract contains fibers of the lateral half of the ipsilateral optic nerve and the medial half of the contralateral optic nerve.

Optic cross component

Components of the optic pathway that form the optic bundle after the optic nerve fibers are partially crossed:

Nerve fibers from the temporal side of the retina do not cross and directly enter the ipsilateral tract; nerve fibers from the nasal side cross to the contralateral tract. Located behind the saddle tubercle, blood is supplied by the branches of the arterial ring. When the middle part of the optic cross itself is damaged, it causes temporal blindness in both eyes, which is more common in the compression of pituitary tumors and craniopharyngioma. Lateral damage causes lateral blindness in one side, which is more common in internal carotid atherosclerosis.

Morphological Structure and Physiological Function

Optic intersection is the intersection and expansion of optic nerves on both sides, which is located on the saddle and is oval or flat quadrangular. The thickness is about 3 to 5 mm, with an average of 4 mm, the front-to-rear diameter is 4 to 13 mm, the average is 8 mm, and the transverse diameter is 10 to 20 mm, the average is about 13.3 mm. The position of the cross on the saddle septum varies from person to person. In normal humans, 5% are located in the sphenoid nerve sulcus, 12% are above the saddle diaphragm, 79% are at the posterior margin of the optic cross, and 4% are behind the saddle. The relationship between the optic cross and surrounding tissues is very important. The pituitary gland below the optic cross is separated by the saddle septum. The pituitary stalk connects the pituitary and the gray nodules in the lower thalamus through the saddle septum. The distance between the optic cross and the saddle septum is 5 to 10 mm, and the optic cross is the cistern. The tumor in the saddle cannot directly oppress the optic cross before the saddle septum. Above the visual cross is the front end of the third ventricle floor. The posterior and inferior sides are adjacent to the visual recess of the third ventricle and the funnel recess, so the expansion of the third ventricle caused by any reason can compress the optic cross and cause a visual field defect; the anterior cerebral artery borrows from the anterior communicating artery Connect here. The optic cross is located anteriorly, and the anterior communication artery is on it. If an aneurysm occurs on the artery, the optic cross is compressed, and the visual field defect in the subtemporal quadrant of both eyes appears. The funnel passes through the saddle septum and extends into the saddle along the posterior margin of the optic cross, continuous with the posterior pituitary lobe; the lateral side of the optic cross is adjacent to the internal carotid artery and posterior communicating artery, and the cavernous sinus is located below it. Therefore, in addition to the diseases of the vision cross, the diseases in the surrounding area can often violate the vision cross and cause the corresponding visual field defect as the basis for localization diagnosis. Nerve fibers in the optic cross include two groups: crossed and non-crossed. The crossed fibers come from the retinal and nasal halves of the two eyes; the non-crossed fibers come from the retinal and temporal halves of the two eyes. The intersecting fibers from the upper part of the retina occupies the upper layer of the visual cross, forming the hind knee on the same side, and then heading to the contralateral visual tract; Sight beam. The non-crossing fibers from the upper half of the retina are located on the inside and above the same side of the retina, and the non-crossing fibers on the same side of the lower half enter the ipsilateral tract. Macular fibers are also divided into two types: crossed and non-crossed. The crossed macular fibers cross to the opposite side at the upper and lower back of the visual cross; the non-crossed macular fibers enter the ipsilateral visual bundle. As a result, different visual field changes can occur in lesions in different parts of the visual intersection, which is clinically significant.

Astigmatism and astigmatism

1. Optic glioma:

Optic glioma is one of the most common primary tumors of the visual pathway. It can be divided into intraorbital type, cranio-orbital communication type, and intracranial type according to the anatomical part. The intracranial type can be divided into three types: type , simple optic nerve type; type , simple optic cross or simultaneous involvement of the optic nerve type; type , involving the hypothalamus or other structural types. The main clinical symptoms are decreased vision, visual field defect and optic nerve atrophy. If the hypothalamus is involved, there may be obesity, growth retardation and precocious puberty, sexual dysfunction and menstrual disorders.

Intracranial optic nerve-optic glioma has more characteristic imaging findings, and MRI shows that the lesions are significantly better than CT. CT plain scan lesions are of equal density or slightly lower density, part of which grows along one side of the optic nerve, and the normal visual cross structure is difficult to show. CT enhanced scans are mostly uniform and moderately enhanced. MRI mainly manifests as long T1 and long T2 signal lesions on the saddle, with clearer borders. The optic nerve or (and) optic cross is thickened or swollen in a spindle shape or mass. A small part may be cystic and calcified. It was moderately and evenly strengthened.

2, visual cross injury: most of the damage caused by frontal force, bone compression is rare, vascular damage may be one of the important reasons. Depending on the location and extent of the injury, different visual field defects and fundus changes can occur.

Retinal retinal tumor

Intracranial congenital tumor:

1. Epidermoid cysts and dermoid cysts:

(I) Organization

Epidermoid cysts and dermoid cysts are generally thought to develop from the attachment of the skin's ectoderm. This kind of attachment is ectopic residues embedded in the skull when the neural tube is closed from the ectoderm and closed 3 to 5 weeks after the embryonic development. If the ectopic occurs in the very early stage, at this time the skin ectoderm has not differentiated into various structures of the skin, then after being embedded, it will differentiate into various components of the skin and form a skin-like cyst; for example, the skin ectoderm cells have differentiated After being embedded, only epidermal tissues develop, forming epidermoid cysts. It is also believed that epidermoid cysts and dermoid cysts have nothing to do with development time. If all layers of skin tissue are ectopic, they develop into dermatoid cysts; if only epidermal tissues are ectopic, they develop into epidermal cysts. Epidermoid cysts contain only one germ layer, the ectoderm component. Dermatoid cysts contain ectoderm and mesoderm components. Teratomas contain three germ layers.

2. Chordoma: The tumor at the base of the skull initially grows out of the epidural, covered with an envelope, and the bottom infiltrates the bone at the base of the skull and invades the nerves. Invasion and destruction of zygomatic tail tumors in the vertebrae and intervertebral bones. Tumors are mostly lobular, with a smooth surface and a lubricating touch, grayish white, ranging in quality from soft to hard. Early demarcations are more clear, and late demarcations are unclear. There are cysts of various sizes on the cut surface, containing translucent jelly-like or mucus-like substances, fibrous tissue separated into small leaflets, which may have calcification, and old bleeding, necrosis and cystic changes are common. Those with soft tumor tissue tend to produce more mucus and tend to be benign, while those with hard tissue may have more calcifications and a greater tendency to malignancy.