Optic Nerve: Structure, Function & Diseases

The optic nerve is responsible for making it possible for people to recognize their environment. Thus, it is one of the most important parts of the eyes. At the same time, different diseases can limit the function of the optic nerve.

What is the optic nerve?

The optic nerve is made up of nerve fibers. These are responsible for the image, which are perceived through the most important sensory organ, to reach the brain. A total of about 1 million nerve fibers combine in the optic nerve. Only when the signals are properly transmitted to the brain, an image is formed. The optic nerve works primarily with incident light. It runs from the eyeballs to the brain. In order to be able to adapt to all movements, it is in an S-shape. Some doctors define the optic nerve less as a nerve and much more with a “pathway” of the brain. Its performance and function can be compared to the white matter of the brain. In addition, the optic nerve is supplied by blood vessels that arise from the soft meninges. The course of the optic nerve has several parts. Before the optic nerves enter the brain, they cross each other. Once the nerves are damaged by disease or external force, serious consequences and discomfort cannot be ruled out.

Anatomy and structure

The optic nerve connects the retina to the brain. Its length measures about four to five centimeters. At the same time, the optic nerve is divided into different sections within the eye. The first section is located in the eyeball and is called the intrabulbar portion. After leaving the eyeball, it opens into the orbit. The intraorbital section is followed by the intracranial section. This is located in the skull. Here, the optic nerve consists of nerve fibers that are bundled together. The nerve fibers originate from the ganglion cells, which can be located in the innermost cell layer of the retina. The optic nerve passes through the eyeball and later leaves it on its way to the brain. The point where the bundled nerve fibers leave the eye is called the optic disc. In the general public, this location is increasingly known as the “blind spot.” The opening where the optic nerve enters the skull is called the canalis opticus. After passing through the orbit, the optic nerve is also surrounded by the tendon ring of the eye muscles. Further on, the optic pathway crosses before the bundled nerve fibers finally reach the brain, thus being able to transmit the received stimuli.

Function and tasks

The optic nerve enables humans to recognize contours, colors, and movements. If it were not present, only a black image would result. Thus, the optic nerve represents a crucial part of the most important sensory organ. The image itself is created by light refraction and various processes on the retina. As soon as light falls on the retina, the irradiations produce certain excitations in the eye. The retina eventually transmits the image, or excitations, to the optic nerve in the form of stimuli or signals. The stimuli are transmitted until they reach the brain and the affected person can recognize his or her environment. Ultimately, the brain is responsible for turning the signals into images. The optic nerve only transmits stimuli and not pre-existing images. In this process, the left hemisphere of the brain processes the information from the right eye and the right hemisphere of the brain converts the signals from the left eye. Fundamental to this process is the previously occurred crossing of the optic nerves. Most often, the function of the optic nerve is not noticed until various diseases or limitations interfere with it. Yet these have the potential to leave permanent damage. As soon as patients experience declining vision or other symptoms, they should not hesitate to consult a doctor. The fact that the optic nerve is the second cranial nerve illustrates its important function.

Diseases and ailments

As soon as the function becomes limited, it is usually necessary to arrange the everyday life differently. Different influences exist that can be responsible for causing damage to the optic nerve. Most commonly, these are exerted by external force. These include, for example, an accident through which the optic nerve is pulled or crushed. This can happen in a car accident, but also by a fist blow in the region of the eye.In such cases, bleeding is usually responsible for the symptoms. These often result from the eye socket and lead to an increase in pressure. As a result of the pressure increase, the optic nerves lose their usual space and bruising may occur instead. In addition to external force, infections are also a possibility. These are often caused by bacteria and viruses and primarily affect the eye socket. However, damage to the optic nerve cannot be ruled out. Inflammation of the optic nerve often occurs in multiple sclerosis, with the part behind the eye in particular being affected by the infection. In addition to movement pain, vision becomes impaired. In some patients, blindness occurs. However, this is not a permanent condition. Despite correct measures, however, it cannot be ruled out that vision will not return to its original state even after the inflammation has subsided. The “glaucoma” causes an increase of pressure in the eye. The vessels through which the optic nerve and retina are supplied suffer squeezing. Serious damage can result from the undersupply.