Sight is one of our most essential senses, probably being the most developed exteroceptive sense in humans. Not in vain, we dedicate a large part of our brain to the processing of visual information, being able to perceive a wide variety of parameters such as color, shape, depth or luminosity with notable acuity and precision.
But in order to process all that information, and in fact to be able to see in general, it is first necessary for the information captured by the eyes to reach the relevant brain nuclei. AND This would not be possible without the existence of the optic nerve which we are going to talk about below.
We give the name optic nerve to a tract or set of nerve fibers that go from the eye to the central nervous system and whose presence allows vision. This tract is part of the cranial nerves, specifically pair II, and consists of more than one million neurons (approximately, it is estimated that around one and a half million) of a sensory type, not transmitting information to the eye but only receiving it from it.
This nerve can be located in a space between the back of the eyeball, having one of its ends in the retinal ganglion cells, on the one hand, and the optic chiasm, on the other This small section, between 4 or 5 cm in length, is of vital importance and without it we would not be able to see.
From the chiasm, most of the fibers of the optic nerves of both eyes will decussate (that is, the one from the left eye will pass to the right hemisphere and vice versa), forming a tract that will go to the lateral geniculate nucleus and from there to different nuclei. of the cerebral cortex.
The optic nerve has the peculiarity that initially the fibers that will make it up (the neurons that connect with the ganglion cells) are not myelinated until they meet in the so-called optic papilla or blind spot, an area where there are neither cones nor rods and from which the neurons will form the optic nerve itself, already myelinated in order to allow rapid and efficient transmission of visual information.
Thus, the optic nerve, which It is made up mainly of myelinated axons, is mainly white matter. Although it originates outside the skull (in the retina), once it enters it and especially in the bony part, the optic nerve is covered and protected by the meninges.
What is it for?
The main function of the optic nerve, as you can already guess, is to transmit the visual information that we capture through the photoreceptors of the retina to the rest of the brain in order to process and interpret it.
First, the photoreceptor captures external information generating a series of electrochemical reactions that in turn will transform the data into bioelectric impulses that will activate the retinal ganglion cells, which in turn will travel to the blind spot where the nerve fibers join to form the optic nerve, the which will proceed to send the message.
Curiously, despite being perhaps the most important nerve when it comes to being able to see, its location in the retina is what causes the existence of our blind spot.
Parts of the optic nerve
Although the optic nerve is relatively small on its journey to the optic chiasm, the truth is that Different segments can be observed on their journey between the eye and the aforementioned chiasm Among them the following stand out.
1. Intraocular segment
This first segment of the optic nerve is the one that still runs inside the eye, in the section that It goes from the ganglion cells to the blind spot and then passes through the lamina or cribriform zone which passes through the sclera and the choroid.
2. Intraorbital segment
This is the part of the optic nerve that goes from the exit of the eye to its exit from the eye sockets. In this part the nerve passes around the muscles that control the eye and the fat after it.
3. Intracanacular segment
It is in this third segment that the optic nerve finally reaches the skull, along with the ophthalmic artery. For this the nerve It will enter through a hole called the optic foramen This area is one of the most sensitive and easy to injure.
4. Intracranial segment
The last of the segments is the intracranial one, in which the optic nerve It is already completely inside the skull and travels to the optic chiasm. It is here where it receives the protection of the meninges.
Pathologies and problems associated with your injury
The optic nerve is one of the most important nerves in our vision and without it, vision as such would not be possible. There are multiple possible conditions that can occur in this nerve and cause us either blindness or alterations and difficulties in vision.
Among them we can find atrophy of the optic nerve derived for example from neuropathy (for example derived from metabolic problems such as diabetes), poisoning, meningitis (remember that the meninges cover this nerve in some portions, so in case of inflammation they could compress it and damage it), strokes or tumors that generate pressure or destroy said nerve.
Another possibility is that the nerve itself becomes inflamed, a condition called optic neuritis that is often linked to infections and autoimmune problems. Accumulations of substances that form so-called bruises may also appear, especially in the head of the optic nerve (the area where it begins in the blind spot).
Lastly, and probably the most well-known and frequent problem that can cause blindness linked to the optic nerve, is glaucoma This disease is derived from a progressive increase in intraocular pressure, which progressively damages the nerve.
