Definition
The optic nerve (med. Nervus opticus) is the strand of “nerve fibers” that transmits signals generated on the retina of the eye to the brain. Strictly speaking, the optic nerve, which doctors refer to as the nervus (Latin for nerve) opticus, is not actually a real nerve at all, but a “pathway” of the brain, since the retina of the eye is a bulge of the brain during embryonic development.
Course of the optic nerve
The retina of the eye consists of several layers, the outermost of which is the layer of visual receptors, the rods and cones. Several cell layers with switching stations for the light-induced electrical signals of the sensory cells connect to the inside. The fibers of the so-called ganglion cells, which are located in the innermost cell layer of the retina, form the actual optic nerve.
The place where these fibers leave the eye as an optic nerve is called the papilla (lat. Papilla Nervi Optici) and is located about 15° from the center of each eye to the nose. Since the fibers have to break through the layer of light receptors to reach the outside, the area of the papilla is not light-sensitive and is also called the “blind spot“.
After leaving the eyeball, the optic nerve traverses the fatty tissue located in the orbit between the muscles of the eye and enters the skull through an opening (Canalis Opticus). In the skull, the optic nerves of both eyes form the optic chiasma (Chiasma Nervi Optici), an area where the fibers that conduct signals from the halves of the eyes facing the nose cross to the other side. Because of the anatomical proximity of this junction to the pituitary gland, the optic nerve junction has a certain significance in the diagnosis of certain brain tumors.
In addition, injuries to the optic nerve before and after the intersection produce different failures in the visual field, which allows the physician to assess the location of damage with little effort. In the further course, the fibers of the left hemisphere of both eyes pull in the left optic nerve and the fibers of the right hemisphere of both eyes pull in the right optic nerve. Since the nerves resulting from the intersection now enter the brain (one in each hemisphere), after the intersection of the optic pathways one no longer speaks of the optic nerve, but of the “visual tract” (lat.
Tractus Opticus). The refraction of the lens of the eye results in the information of the other side of the visual field reaching each half of the brain. Everything we see on the right side of our visual field is processed in the left hemisphere of the brain and vice versa. The fibers of the optic nerve end in the cerebral cortex at the back of the head, where the information processing of the perceived takes place.
