Optic Neuritis - Symptoms, Causes & Treatment

What is Optic Neuritis?

Optic neuritis (ON) is the inflammation of the optic nerve, a bundle of nerve fibers responsible for central vision. The optic nerve transmits signals from the eye's retina to the brain for interpretation. This enables you to see and recognize whatever is in your field of view.

Inflammation or irritation of the optic nerve affects how these signals are transferred to the brain. This causes vision problems such as color blindness and blurry vision. It may also result in the swelling of one or both eyes. However, it mostly affects one eye. 

Anyone can get optic neuritis, but it's common among those living with multiple sclerosis (MS). The annual incidence of optic neuritis in the United States is about 5 cases per 100,000 people.¹

Although some symptoms of ON may seem scary, most people recover without treatment. 

Symptoms of Optic Neuritis

Some people may not show any visual signs. Those that do may show symptoms such as:

• Loss of vision in one eye for an hour to a few hours
• Pain around the eye that worsens with eye movement
• Changes in the pupil's reaction to light
• Blurry vision when your body temperature increases, e.g., after a workout session
• Flashing or flickering lights with eye movement
• Loss of color vision

Optic neuritis symptoms may vary in severity from one person to another—severe inflammation results in more noticeable symptoms.

Causes of Optic Neuritis 

The exact cause of optic neuritis is unknown. However, experts believe it results when the immune system mistakenly targets the myelin sheath, the substance covering the optic nerve. The myelin sheath insulates the optic nerve like the plastic covers on electric cables. 

If damaged by inflammation or swelling, the transmission of electrical signals from the eye to the brain is disrupted. This may result in short or long-term vision loss.

A common condition associated with ON is multiple sclerosis (MS). This is a disease where the immune system targets the nerves in your central nervous system, including the optic nerve. It causes damage to the myelin sheath. Studies indicate that 15 to 20 percent of people with MS have neuritis (nerve inflammation) as one of the symptoms.³

Other conditions linked with inflammation of the optic nerve include:^{4, 5}

• Neuromyelitis optica (NMO), or Devic's disease. It damages the nerves of the eyes and spinal cord.
• Myelin oligodendrocyte glycoprotein (MOG) antibody disorder. It causes inflammation of the optic nerve, spinal cord, and brain.
• Lupus. It causes inflammation in many parts of the body, including the central nervous system (CNS).
• Sarcoidosis. Growth of inflammatory cells known as granulomas in many parts of the body, including the eyes.
• Behçet disease. It causes blood vessel inflammation throughout the body, including the eyes.

Other causes of severe optic neuritis include:

• Fungal infections such as Cryptococcosis
• Bacterial infections such as tuberculosis (TB), meningitis, or syphilis
• Viral infections such as measles, mumps, chickenpox, herpes zoster, viral encephalitis, etc
• Respiratory infections such as mycoplasma pneumonia, common cold, pharyngitis, epiglottitis, etc
• Exposure to toxic substances such as drugs and chemicals
• Vitamin B12 (cobalamin) deficiency

Who is at Risk for Optic Neuritis?

You're more likely to get optic neuritis if you are:

• Aged between 20 to 40 years
• Female (three times more likely than men)
• Of Caucasian origin (white)
• Have multiple sclerosis 
• Live in a high-altitude area
• Have certain genetic mutations

When to See an Eye Doctor

Eye pain due to optic neuritis goes away after a few days, and most people with disturbed vision will realize an improvement. 

However, some may be left with blurry, dark, dim, or distorted vision. In severe cases, complete vision loss may occur. Vision usually improves over a few weeks to a month.

Seek medical attention if you experience the following:

• Pain that gets worse with time
• Significantly decreased vision
• Double vision (diplopia)
• Flashing lights
• Weakness or numbness in limbs
• Progressive vision loss

How Your Doctor Diagnoses Optic Neuritis

Your doctor will perform a complete medical exam to observe the presence of optic nerve inflammation and its causes. Expected tests include:

• Color vision testing
• Magnetic resonance imaging (MRI) of the brain to create images of the optic nerve
• Visual acuity testing using a Snellen chart
• Visual field testing
• Direct ophthalmoscopy to examine the optic disc

Other tests may include:

• Pupillary reaction test to test how your pupils respond to light 
• Blood tests to investigate the presence of disease-related proteins 
• Lumbar puncture (spinal tap) to check the fluid in your brain and spinal cord 
• Optical coherence tomography (OCT) to measure retinal nerve thickness (someone with optic neuritis will have a thinner one)
• Visual evoked response test to measure the speed at which signals travel through the optic nerve to the brain 

Treatment Options for Optic Neuritis

Someone with optic neuritis will recover their vision within 2 to 3 weeks without treatment. 

Intravenous (through the vein) corticosteroids such as methylprednisolone or oral corticosteroids such as prednisone can ease inflammation and speed up recovery.⁷ However, they will not affect the final visual quality. 

If the cause of optic neuritis is an underlying condition such as multiple sclerosis, lupus, or microbial infections, your doctor will recommend the appropriate treatment.

If the diagnosis shows Vitamin B12 deficiency in the body, your doctor may prescribe Vitamin B12 shots to supplement your nutrition.

It's important to closely monitor the symptoms of optic neuritis and seek early treatment to avoid disease progression.

Complications If Left Untreated

If left untreated, symptoms of optic neuritis may be severe, including optic nerve damage. 

Other complications may include:

• Progression to multiple sclerosis
• Complete vision loss
• Nerve problems in other body parts

Outlook for Optic Neuritis

Optic neuritis symptoms generally improve in about 80 percent of people over a few weeks.⁸ However, some symptoms, such as reduced vision, may persist after recovery. 

Sometimes, optic neuritis may occur without either multiple sclerosis (MS) or neuromyelitis optica (NMO), causing a disorder known as chronic relapsing inflammatory optic neuropathy (CRION). CRION is associated with more intense pain and discomfort than optic neuritis occurring alongside MS. There is also a significant risk of blindness with CRION.⁹

Fortunately, CRION responds well to intravenous (IV) steroids, and oral steroids or other medications may be taken for extended periods to avoid recurrence.