What Is Optic Neuritis and Can It Cause Vision Loss?

Optic neuritis is an inflammation of the bundle of nerves that connects your eye to your brain, called the optic nerve. When the optic nerve is inflamed, visual information to the brain is disrupted, resulting in visual disturbances, vision loss, and eye pain.

Optic neuritis is most commonly associated with multiple sclerosis (MS) but can also occur with optic nerve infections or autoimmune diseases. The condition can be diagnosed with an eye exam, imaging studies, and nerve transmission tests. Optic neuritis can often improve with a course of steroid drugs or immunosuppressants.

Symptoms

Although there are many different causes of optic neuritis, the signs and symptoms tend to be the same. With that said, some people may experience mild or fluctuating symptoms, while others may have a debilitating loss of vision.

Optic neuritis usually affects one eye but sometimes affects both (or starts in one eye before "spreading" to the other). Symptoms tend to get worse when your body temperature rises.

Symptoms of optic neuritis include:

• Sudden blurring or "fogginess"
• A sudden or gradual loss of vision, either partial or complete
• Eye pain with movement
• Visual disturbances, such as changes in color (dyschromatopsia) or flashes of light (photopsia) with eye movement
• Loss of peripheral vision
• A blind spot in the central vision
• Loss of depth perception
• Reduced night vision
  

With MS, a person may also experience twitching, a loss of coordination, eye redness, and slurred speech before or during visual symptoms. Light sensitivity (photophobia) can also occur.

Children tend to experience less eye pain than adults but are more prone to blurring and fogginess.

Types and Causes

Inflammation of the optic nerve (also known as the second cranial nerve or cranial nerve 2) can be caused by many different things. The causes can be broadly categorized as being either "typical optic neuritis" or "atypical optic neuritis."

Typical Optic Neuritis

Typical optic neuritis is inflammation of the optic nerve caused by demyelination. This is the deterioration and loss of the insulating coating of nerves, called the myelin sheath, that helps electrical signals move smoothly from one nerve cell to the next.

Multiple sclerosis (MS) is the primary cause of typical optic neuritis. This autoimmune disease is characterized by the demyelination of the central nervous system, leading to the dysfunction of many organ symptoms. Studies have found that up to 50% of people with MS will develop optic neuritis during the course of their disease.

Demyelination of the optic nerve can sometimes occur for no known reason, referred to as idiopathic optic neuritis. Some research suggests that the condition may simply be a precursor to MS.

Atypical Optic Neuritis

Atypical optic neuritis is the inflammation of the optic nerve caused by conditions other than MS. The ways that these conditions cause optic neuritis can differ significantly.

Causes of atypical optic neuritis include:

• Viral infections of the optic nerve: Examples include measles, mumps, eye herpes, shingles (herpes zoster), and cytomegalovirus (CMV).
• Bacterial infections of the optic nerve: Examples include Lyme disease, cat scratch fever, bacterial meningitis, tuberculosis, and neurosyphilis.
• Glaucoma: This is a group of conditions that cause vision loss due to optic nerve damage. High eye pressure, also known as ocular hypertension, is the primary cause.
• Autoimmune diseases: Lupus, rheumatoid arthritis, Sjogren's syndrome, and sarcoidosis are among the most common causes.
• Behcet's disease: This is an idiopathic form of vascular inflammation (vasculitis) that may affect blood flow to the optic nerves.
• Neuromyelitis optica spectrum disorders (NMOSD): This is a poorly understood autoimmune condition that acts similarly to MS but does not involve the same immune antibodies.
• Elevated intracranial pressure: This is increased pressure inside the skull that can compress and injure the optic nerves. Causes include head injury, brain tumors, meningitis, and acute liver, kidney, or heart failure.
  

Diagnosis

Optic neuritis is typically diagnosed by an eye specialist known as an ophthalmologist. The diagnosis starts with a review of your medical history and an eye exam.

The eye exam usually involves dilating eye drops that allow the specialist a better view of the inner eye with a lighted magnifying tool known as an ophthalmoscope. In addition to testing your central vision, the exam will include e a visual field test to check your peripheral (side) vision.

Other tests used to diagnose optic neuritis and its underlying cause include:

• Magnetic resonance imaging (MRI): This non-radioactive imaging study is better able to detect soft tissue injuries, including those involving the optic nerve.
• Optical coherence tomography (OCT): This non-invasive imaging method uses reflected light to create pictures of the back of your eye.
• Visual evoked potential (VEP): This test involves the placement of electrodes on your scalp to measure electrical signals generated by your brain in response to visual stimulation.

Treatment

Many people with optic neuritis improve without treatment and after the underlying cause resolves. Treatment often depends on how soon the condition is diagnosed after you first notice symptoms.

Not all causes are curable and are more likely to need ongoing management to reduce the frequency or severity of symptoms and avoid permanent vision loss. Examples include:

• Corticosteroids: These drugs given orally (by mouth) or intravenously (into a vein) can quickly ease optic nerve inflammation. Intravenous methylprednisolone is preferred for MS. Common side effects include mood changes, insomnia, swelling, headache, stomach upset, skin changes, and an increased risk of infection. The effectiveness of the drugs tends to wane over time.
• Immunosuppressants: These medications are commonly used to control autoimmune disorders like MS and lupus. These include older drugs like azathioprine and methotrexate and newer ones like Gilenya (fingolimod) and Aubagio (teriflunomide). Common side effects include headache, stomach upset, drowsiness, hair loss, easy bruising, and weight gain.

With treatment, your vision may return to normal or close to normal within six months.

Summary

Optic neuritis is the inflammation of the optic nerve, most commonly the result of multiple sclerosis. It can also be caused by optic nerve infections, autoimmune diseases, and conditions associated with elevated eye or intracranial pressure.

Optic neuritis can cause sudden blurring, vision loss, visual disturbances, and eye pain which may resolve on its own without treatment. Other causes, including MS, may require intravenous corticosteroids or oral immunosuppressants to ease optic nerve inflammation and prevent recurrence.