Anatomy & Organs

Visual pathway – structure, function & diseases

Visual pathway

The visual pathway is understood to mean special somatosensitive fibers that run from the retina of the eye to the visual cortex of the brain . Human vision is made possible by the complex structure of the visual pathway.

What is the optic pathway?

The visual pathway is a part of the brain. All components have their origin in this body region. This also includes the optic nerve (Nervus opticus), which also represents a part of the visual pathway. The neuronal interconnection of the optical system takes place via the visual pathway.

Special somatosensitive fibers are guided from the retina in the direction of the brain. The first link of the visual pathway is formed by the photoreceptor cells of the retina, which receive incoming light stimuli. The cell bodies of the photoreceptor cells are located in the outer layer of the granule. They are considered the first neuron (nerve cell). From them, the nerve impulses go via the second neuron in the inner granular layer in the direction of multipolar retinal nerve cells within the stratum ganglionare.

The third nerve interconnection level is established by these ganglion cells. With their long processes, they form the optic nerve. The first switching of the incoming nerve impulses already takes place within the retina.

Anatomy & Structure

The human visual pathway has a complex structure. It extends from the posterior poles of the eyes to the cortex of the cerebrum . The retinal ganglion cells, which unite to form the optic nerve, reach their exit in the orbit (eye socket). The optic nerve is then made up of two different fiber bundle parts.

In the right eye, the outer (lateral) part of the retina is on the right side, while the nasal part is on the left. In the left eye it is exactly the opposite. The fiber bundles of the retinal nerve cells of the respective eye attach themselves to one another and cross one another. A little later they come together in another combination. The branch point is called the chiasma opticum . This is where the fibers of the nasal retina cross.

Following the crossing, the fibers of the corresponding retinal sides run within the optic tract. While the right optic tract carries the fibers of the right halves of the retina, this is the case with the left optic tract with the left halves. The crossed fibers of the right eye and the uncrossed fibers of the left eye form a union in the left optic tract. This corresponds to the right side of the face. The crossed fibers of the left eye and the uncrossed fibers of the right eye, on the other hand, form their union within the right optic tract, which corresponds to the left side of the face.

The human visual fields are reflected in opposite directions by the sections of the retina. This means that the right part of the visual field of the eyes is recorded on the left side of the retina. In contrast, the right half of the retina forms the left half of the visual field.

Switching between the right and left optic tract takes place in the midbrain . From there, the so-called visual radiation goes in the direction of the cerebral cortex. Its end is located within the meningeal flap in the visual center on the inside of both cerebral hemispheres.

Function & Tasks

The visual pathway fulfills the function of transmitting visual impressions and signals from the eye to the brain. In this way, the perception of sensory impressions is made possible. Without the transmission of electrical signals to the cerebrum, humans would not be able to register the impressions they see.

Furthermore, there is a coupling between the visual pathway and the sense of balance as well as the righting reflexes. If an eye impression deviates from the vestibular system, the righting reflex compensates for this. For example, if a person is standing on a swaying ship, the fluctuations are perceived by the eyes and the vestibular system. By activating the appropriate muscles, man can continue to stand firmly. The visual pathway is divided into three functional systems. These are color and shape vision (parvocellular system), motion vision (magnocellular system) and optomotor function (koniocellular system).

Diseases

The visual pathway can be affected by various injuries or diseases. This usually creates too much pressure on the visual pathways or there is an insufficient blood supply.

Possible reasons for this are bleeding , degenerative processes, injuries, inflammation, tumors , reduced blood flow or interruption of blood flow. Another possible cause is an aneurysm , which is a bulging or widening of an artery .

Damage to the visual pathways can cause visual field defects in affected individuals , depending on which visual pathway area is affected. If there is a lesion in the optic nerve that causes it to be disrupted, unilateral blindness will result. Doctors then speak of amaurosis. The most common causes of this damage are optic neuritis or papillae disease.

A bilateral half visual field loss on the outer side of the face shows up in a chiasma syndrome, which is also known as the blinder phenomenon. It is usually caused by tumors that put pressure on the optic nerve crossing. Other conceivable causes are syphilis or multiple sclerosis . A quick operation makes it possible to reverse the visual field defects. Otherwise there is a risk of further visual disturbances .

A lateral compression of the chiasm, which medical professionals refer to as heteronymous binasal hemianopsia, results in equilateral hemi-blindness. The reason for this is damage to the uncrossed nerve fibers. Sclerosis of the internal carotid artery or a bilateral aneurysm are usually responsible. In the case of ophthalmic migraines , ciliated scotomas are possible, which can be accompanied by headaches , dizziness , flashes of light, nausea and vomiting . In some cases, those affected also suffer from paralysis of the eye muscles. The reason for this is temporarycirculatory disorders .

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.