Experts also call the optic nerve the optic nerve or second cranial nerve. It occupies the middle part of the so-called visual pathway, via which the image travels from the eye to the brain.
The retina generates excitation in the eye when light is shone on it. The optic nerve transmits these excitations (electrical potentials) to the brain. The brain interprets the signals as images, which enables us to see our surroundings.
The human optic nerve is around four to five centimetres long and consists of bundled nerve fibers. The pathway leads from the sieve plate (lamina cribrosa) via the sclera to the optic nerve junction. Experts also call it the optic chiasm.
Three different sections divide the optic nerve of the eye:
- Intrabulbar section: the part of the optic nerve inside the eyeball
- Intraorbital part: The part of the optic nerve inside the eye socket
- Intracranial part: The optic nerve runs inside the skull (cranium)
The optic nerve in the eye also consists of around one million nerve fibers. These fibers are known as axons. The extensions of the retinal ganglion cells are called optic nerve fibers. The individual axons unite to form the optic nerve.
Visual impressions that we perceive with our eyes reach the brain via the optic nerve (nervus opticus) @ bilderzwerg /AdobeStock
The retina of the eye consists of several layers:
The outer layer forms the visual receptors, the rods and the cones in the eye. This outer layer is followed by several thin layers in the eye, which are equipped with so-called switching stations. These cell layers are responsible for the electrical signals of the sensory cells generated by the light.
The inner cell layer of the retina also contains fibers of the so-called ganglion cells. These fibers form the actual optic nerve in each person's eye. They all leave the eye together at a certain point, the so-called optic disc, as the optic nerve.
The optic disc is not sensitive to light because the optic nerve passes through light receptors and is considered a "blind spot" in the visual field.
After leaving the eyeball, the optic nerve passes through fatty tissue inside the eye socket (orbit). This is located in the eye socket between the muscles of the respective eye.
The optic nerve finally enters the human skull through an opening (canalis opticus). This is where both optic nerves of the eyes meet and form the optic tract junction.
The optic tract junction is an area where the fibers cross each other. Due to the refraction of light at the lens of the eye, the information from the individual hemispheres of the brain come together. The visual pathway cross is therefore an important intersection. Without this intersection in the eye, coordinated vision would not be possible.
The visual pathway junction is therefore located near the pituitary gland. The optic nerves that cross here are therefore of particular importance in the diagnosis of a brain tumor.
The visual pathway simplified
The fibers of the right half of both eyes now run into the right optic nerve. The left fibers of both eyes run together into the left optic nerve. Here the nerves that enter the brain are no longer called the optic nerve but the optic tract.
Ultimately, the optic nerve ends in the cerebral cortex at the back of the head. This is where all the information transmitted from the optic nerve to the brain is processed. Only now can we see.Diseases of the optic nerve often cause visual impairment. They can therefore usually be recognized quickly. The patient does not experience any pain as a result of the disease.
In some diseases, the visual impairment can occur suddenly. Those affected lose their vision within a very short time. With other diseases, however, the process is gradual.
Inferring diseases from visual field loss
A disease of the optic nerve often results in visual field loss. The reason for this is the proximity of the visual pathway junction to the pituitary gland. It does not matter whether the damage to the optic nerve occurs before or after the crossing of the visual pathways.Depending on this, different areas of the visual field are usually affected. The ophthalmologist can draw conclusions about the disease based on the type of visual field loss. Diagnosis is therefore easy. The optic nerve can therefore be treated quickly.
Negative scotoma plays a particularly important role in optic nerve disease in the eye. With negative scotoma, patients can no longer clearly recognize structures in the visual field.The reason for distorted vision is due to a disease of the optic nerve, but always points to other diseases. However, it is possible that the optic nerve is also diseased.
If the patient notices any defects or foreign bodies in the field of vision, they should inform the doctor treating them immediately. This is the only way to make a reliable and rapid diagnosis.
The diagnosis is problematic if
no visual field defects are noticeable. The doctor then has no clues as to the exact disease. Other examination methods also provide little information about the disease of the optic nerve. It is therefore difficult to find a suitable treatment method.The term
optic atrophy refers to
tissue atrophy of the optic nerve. There can be various causes for this atrophy. One reason may be that the patient suffers from
glaucoma.
Excessive intraocular pressure puts pressure on the optic disc, causing it to literally hollow out. This causes the nerve cells in the optic disc to gradually die off. The optic nerve is severely damaged and the loss of vision cannot be restored.
Glaucoma is the most common disease of the optic nerve @ Alessandro Grandini /AdobeStockA common disease of the optic nerve is the so-called congestive papilla. This is an edema, an accumulation of water, which usually occurs in the optic discs of both eyes at the same time. The cause of water retention is increased intracranial pressure, for example due to a brain tumor.
Symptoms of a congestive optic disc include headaches and, later on, visual disturbances. You should always have this examined by a specialist.
If you suffer from a congestive papilledema, it is necessary to find the cause, otherwise serious brain damage can occur.
The disease progresses in several stages:
- In the early stages of a congestive papilla, the edge of the papilla is usually blurred, while the papilla itself is heavily supplied with blood. Vision is rarely impaired at this stage of the disease.
- In the acute stage of optic nerve disease, the optic disc becomes very swollen. The edges of the optic disc also begin to bleed in the form of spokes. The optic disc now has a reddish to grey-reddish color and shows grey deposits. The dent in the eye known as the "blind spot" gradually disappears.
- Experts also call the last stage the atrophic phase. Here, the fibers of the optic nerve in the eye gradually die off. It is only at this stage that the affected person begins to notice the first visual losses.
Inflammation of the optic nerve in the eye occurs quite frequently. Here too, edema develops on the optic disc of the eye. However, this oedema usually goes unnoticed if there is inflammation of the optic nerve outside the eyeball.
The inflammation quickly becomes noticeable in patients: Visual field loss occurs suddenly and pain during extreme eye movements is also very distressing for those affected.
In addition, red-green weakness often occurs and the pupillary reflex no longer functions properly.
Infections and inflammation of the eye and paranasal sinuses are responsible for inflammation of the optic nerve in the eye. However, autoimmune diseases and poisoning are also possible causes.Anterior ischemic optic neuropathy (AION, colloquially "eye infarction") refers to an acute undersupply of oxygen and nutrients to the optic nerve head. Loss of vision occurs very quickly. Patients should therefore consult a doctor quickly.
The undersupply can cause severe damage that cannot be reversed after just a few hours.
Inflammation of a
vessel (vasculitis, e.g. giant cell arteritis) is also a possible cause. This is mainly manifested by a
pulsating temporal artery. In addition, affected persons usually complain of
severe headaches. The scalp can also cause pain. Vasculititis is particularly dangerous as
arteries in the brain can also be affected. For this reason, it is treated with
cortisone.Optic nerve disease can also be caused
by hereditary factors. In this case, the optic nerve generally loses substance. This is particularly the case with optic nerve diseases such as
Behr optic atrophy, Leber optic atrophy and waxy yellow optic atrophy.
Toxins can also damage the optic nerve, which drastically impairs the vision of the person affected.
The visual pathway simplified
