The optic nerve (Nervus Opticus): Function & diseases of the optic nerve in ophthalmology

It is only a few millimetres thick, consists of around one million nerve fibers – and without it we would not be able to see: the optic nerve. As the connection between the eye and the brain, it plays a central role in the human visual system. But what exactly does the optic nerve do? How does it work? And what happens when it becomes diseased? In this overview, we show what the optic nerve does, how it is integrated into the eye, which diseases can affect it – and what this means for a planned laser eye treatment or lens replacement, for example. An in-depth look at an often underestimated but vital part of our vision.

What is the optic nerve – and what role does it play in vision?

The optic nerve – also known medically as the nervus opticus or nervi optici – is the crucial link between the eye and the brain. It consists of around one million nerve fibers, all of which originate from the retina.

How the optic nerve works together with the brain and retina

Its main task is to receive the visual stimuli generated there in the form of electrical signals and transmit them to the visual center in the cerebral cortex, where they are then processed into an image.

Without the optic nerve, vision would not be possible – even if the eyeball, lens and retina are intact. It transmits what the eye sees to the brain, where colors, shapes, movements and contrasts are created. The nerve fibers run from the posterior pole of the eye – the so-called papilla nervi optici or optic nerve papilla – via the eye socket, through the optic canal to the optic chiasm and further along the visual pathway (optic tract) towards the brain.

The optic nerve is therefore one of the twelve cranial nerves – and plays a central role in ophthalmology when it comes to assessing visual acuity, visual field and eye health. Even the slightest damage to the optic nerve –whether due to inflammation, pressure or circulatory disorders – can lead to considerable visual impairment.

Structure and function of the optic nerve

The optic nerve is a highly specialized part of the central nervous system – and also one of the most important cranial nerves. It is around four to five centimetres long, runs from the eyeball through the bony eye socket and ends in the brain. Despite its name, the optic nerve is not actually a peripheral nerve, but a protrusion of the diencephalon, which emphasizes its close connection to the central nervous system.

Structure at a glance:

• Optic disc (optic nerve head): The visible exit point of the optic nerve at the back of the eye – medically referred to as the papilla nervi optici or discus nervi optici.
• Intraocular part: About 1 mm long, inside the eye – this is where the optic nerve begins at the retina.
• Intraorbital section: Inside the eye socket, where the optic nerve runs in a slight S-shaped loop to follow movements of the eye.
• Canalicular section: Narrow passage through the optic canal where it crosses the bony base of the skull.
• Intracranial section: Runs to the optic chiasm, where fibers from both eyes cross.

Diseases of the optic nerve – when the “signal” is disturbed

As the central link between the eye and the brain, the optic nerve is a sensitive structure that can be impaired by disease or damage. These often have massive consequences:

Glaucoma – the most common damage to the optic nerve

Glaucoma, also known colloquially as glaucoma, is one of the most common and most dangerous diseases of the optic nerve. It is not a single disease, but a group of eye diseases that lead to gradual damage to the optic nerve – in many cases triggered by increased intraocular pressure.

How does the damage occur?

The pressure in the eye is created by the aqueous humor, which is produced and drained in a natural cycle. If the drainage is obstructed, the pressure in the eyeball can increase. This increased pressure places particular pressure on the sensitive area of the optic nerve head (optic disc) and disrupts the blood supply to the nerve fibers there. The result: irreversible damage, which initially manifests itself in visual field loss and, in the later stages, can lead to massive loss of vision and even blindness.

Glaucoma is treacherous:

• In most cases, it is asymptomatic for a long time.
• Changes to the optic nerve can often only be detected by an early ophthalmologic examination.
• The damage cannot be reversed, but its progression can be halted with timely treatment.

Treatment and prognosis:

The aim of any glaucoma therapy is to reduce the intraocular pressure – depending on the severity, with eye drops, laser procedures or surgical interventions. Regular checks of the optic nerve and visual field function arecrucial to ensure that further optic nerve damage is prevented.

Other optic nerve diseases such as optic neuritis, atrophy & co

In addition to glaucoma, there are a number of other diseases that can affect the optic nerve – some acute, some gradual. Depending on their location and severity, they lead to loss of vision, visual field defects or color vision disorders.

An overview of common optic nerve diseases:

• Optic neuritis (optic nerve inflammation)
  Mostly inflammatory, often as part of multiple sclerosis, less frequently due to infections. Symptoms: visual deterioration, color vision impairment, pain when moving the eyes.
  Treatment: High-dose cortisone therapy, further neurological clarification if necessary.
• Papillitis
  Acute inflammation of the optic nerve head, often associated with swelling of the optic disc.
  Treatment: Depends on the cause (infectious, autoimmune), usually anti-inflammatory.
• Optic atrophy
  Degeneration of nerve fibers, often the result of untreated diseases (e.g. glaucoma, circulatory disorders).
  Treatment: No cure possible, focus on preventing further damage.
• Congestive papilla
  Swelling of the optic nerve due to increased intracranial pressure – e.g. in the case of tumors, bleeding or cerebrospinal fluid outflow disorders.
  Treatment: Cause-oriented, often interdisciplinary with neurology/neurosurgery.
• Ischemic optic neuropathy (NAION)
  Circulatory disorder of the optic nerve head, usually due to high blood pressure, diabetes or a drop in blood pressure at night.
  Treatment: No specific therapy – risk factor control and, if necessary, measures to promote blood circulation are important.
• Retrobulbar neuritis
  Inflammation of the optic nerve behind the eyeball, often painful, with acute loss of vision.
  Treatment: Similar to optic neuritis, often in the context of MS, with cortisone.

Symptoms and warning signs of damage to the optic nerve

Damage to the optic nerve can manifest itself gradually or suddenly – depending on the cause, location and progression of the optic nerve disease. As the optic nerve connects the eye to the brain, disturbances in signal transmission often lead to visual impairment, visual field defects or color vision disorders.

Typical symptoms:

• Deterioration of visual acuity, especially in one eye
• Visual field defects, e.g. dark areas or “blind spots”
• Color vision problems – colors appear paler or distorted
• Pain with eye movement (especially with inflammations such as optic neuritis)
• Flashes of light or flickering
• Relative afferent pupillary deficit (RAPD) – the affected pupil reacts to light with a delay
• Feeling of pressure or dull pain behind the eye

In the case of progressive damage, e.g. due to glaucoma, central vision is initially retained – at first there are marginal losses in the visual field, which often go unnoticed.

Take warning signs seriously:

• When sudden vision loss occurs
• In the event of persistent visual impairment in one eye
• If there is a distortion of colors or contrasts

What role does the optic nerve play in laser eye surgery?

During laser eye treatment – for example with Femto-LASIK, Trans-PRK or SmartSight – the shape of the cornea is changed in order to correct an existing visual defect such as short-sightedness, long-sightedness or astigmatism. The optic nerve itself is not treated directly – yet it plays a decisive role in the success of the procedure.

• The optic nerve is responsible for transmitting signals from the retina to the brain. Only if this line is intact can the brain correctly process the improved light conditions due to the reshaped corneal profile.
• If there is damage to the optic nerve (e.g. due to glaucoma or optic neuritis), the quality of vision may remain impaired even after a perfectly performed laser treatment.

Therefore, the following applies before lasering:

• The optic nerve is thoroughly examined at every aptitude test – including by funduscopy, OCT and, if necessary, visual field examination.
• If there are indications of optic nerve damage, laser treatment cannot be recommended – or alternatives such as lens implants can be discussed on an individual basis.