The optic nerve is responsible for transmitting the signals that the eye perceives to our brain. The brain will then interpret these signals coming from external stimuli in order to form a mental image of what we are seeing.
The optic nerve is composed of approximately 1.2 million axons that originate in the retina’s ganglion cells and which join together as a bundle at the back of the eyeball. The retina, the innermost layer of the eyeball, contains cells called photoreceptors, which transform the perception of light into electrical impulses that then travel along the optic nerve. The cones are the photoreceptors that allow us to see colours, and the rods are involved in the perception of shapes in low light conditions.
These nerve bundles are accompanied by blood vessels that feed them and by supportive glial tissue. The optic nerve is covered by the meningeal sheath and surrounded by cerebrospinal fluid from the point where it leaves the eyeball along its entire length through the central nervous system.
The total length of this nerve is approximately 5 centimetres.
This component of the eye is, therefore, essential for vision, since, even if the eyeball and all the parts that make it up are in perfect condition (the cornea, iris, lens, vitreous humour, retina), if an injury occurs to the optic nerve it will cease to transmit information to the brain and we will not be able to perceive images.
Nerve tissue does not regrow or regenerate, so if the fibres of the optic nerve die the resulting vision loss will be irreversible.
A very common cause of injury to the optic nerve is glaucoma, a disease in which the fibres of the optic nerve die due to an increase in pressure within the eye, this causes the vision to become hazy and reduces the visual field and can even lead to blindness.
Another cause of a serious loss of vision is ischemic optic neuropathy, which is the death of the optic nerve bundles due to a failure or deficiency in the blood supply. The optic nerve can also be damaged by diseases of the central nervous system (multiple sclerosis, tumours, vasculitis), toxins, exposure to radiation, genetic diseases, drugs and as result of trauma.