Optic nerve: parts, pathway and associated diseases

Sight is one of our most essential senses, being probably the most developed exteroceptive sense in humans. Not in vain, we devote a large part of our brain to processing visual information, being able to perceive a wide variety of parameters such as color, shape, depth or brightness with remarkable sharpness and precision.

But in order to be able to process all this information, and indeed to be able to see in general, the information picked up by the eyes must first reach the relevant brain nuclei. I this would not be possible without the existence of the optic nerve, Which we will discuss below.

    Optic nerve: basic description and location

    We call the optic nerve a tract or a collection of nerve fibers that run from the eye to the central nervous system and the presence enables vision. This treatment is part of the cranial nerves, more precisely of pair II, and consists of more than a million neurons (approximately estimated at around a million and a half) of the sensory type, not transmitting information to the eye. but only receiving from him.

    This nerve may be located in a space between the back of the eyeball, bearing one of its ends in the ganglion cells of the retina, on the one hand, and the optic chiasm, on the other hand. This small stretch, between 4 and 5 cm long, is of vital importance and without it we would not be able to see.

    From the chiasm, most of the optic nerve fibers in both eyes will disconnect (that is, the one from the left eye will reach the right hemisphere and vice versa), forming a treatment that will go to the nucleus. lateral geniculate and from there to different nuclei of the cerebral cortex.

    The optic nerve has the peculiarity that initially the fibers that compose it (the neurons that connect to the ganglion cells) are not myelinated until they meet in the so-called optic papilla or blind spot, an area where there are no cones or canes and from which the neurons will form the optic nerve itself, already myelinated to allow rapid and efficient transmission of visual information.

    So the optic nerve, which it consists mainly of myelinated axonsThis is mainly white matter. It always comes from outside the skull (in the retina), once inside and especially in the bony part the optic nerve is covered and protected by the meninges.

      Why is it?

      The main function of the optic nerve, as you can guess, is to transmit the visual information that we pick up through photoreceptors in the retina to the rest of the brain for processing and interpretation.

      First of all, the photoreceptor captures external information, Generating a series of electrochemical reactions which in turn will transform the data into bioelectrical impulses which will activate the retinal ganglion cells, which in turn will move to the blind spot where the nerve fibers come together to form the optic nerve, which will proceed to the ‘sending a message.

      Interestingly, although this may be the most important nerve to be able to see its location in the retina, it is what causes our blind spot to exist.

      Parts of the optic nerve

      While the optic nerve is relatively small in size on its journey to the optic chiasm, the truth is that they can observe different segments of their journey between the eye and the aforementioned chiasmus. These include the following.

      1. Intraocular segment

      This first segment of the optic nerve is what still passes inside the eye, in the stretch that passes from ganglion cells to the blind spot, then passes through the slide or sieve area, Which crosses the sclera and the choroid.

      2. Intraorbital segment

      It is the part of the optic nerve that goes from the exit of the eye to its exit from the sockets. In this part the nerve it goes around the muscles that control the eye and the fat after.

      3. Intracanacular segment

      In this third segment, it is in which the optic nerve finally reaches the skull, next to the ophthalmic artery. For this, the nerve it will enter through an opening called the optic foramen. This area is one of the most sensitive and the easiest to injure.

      4. Intracranial segment

      The last of the segments is the intracranial, in which the optic nerve it is already totally inside the skull and moves to the optic chiasm. This is where you get brain protection.

      Pathologies and problems associated with their injury

      The optic nerve is one of the most important of our visual and it is that without it, the vision as such would not be possible. There are many possible conditions that can occur in this nerve and cause 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 like diabetes), intoxication, meningitis (remember that the meninges cover this nerve in some portions, so in case of inflammation could compress and damage it), strokes or tumors that generate pressure or destroy this nerve.

      Another possibility is that the nerve itself becomes inflamed, a condition called optic neuritis which is often linked to infections and autoimmune problems. Accumulations of the substances that form the so-called blisters can also appear, especially at the head of the optic nerve (the area where it begins at the blind spot).

      Finally, and probably the most common and most common problem that can lead to optic nerve blindness, is glaucoma. This disease is caused by a gradual increase in intraocular pressure, which gradually damages the nerve.

      Bibliographical references:

      • Miller, NR and Newman. NJ (eds) (2005) .. Clinical Neuroophthalmology by Walsh and Hoyt. 6th edition. Baltimore: Williams and Wilkins, 385-430.
      • Sánchez, F. (2001). The optic nerve and visual disturbances. Integral medicine, 38 (9): 377-412. Elsevier.

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