Understanding Optic Neuritis

Optic neuritis is an eye condition that causes the optic nerve to become inflamed. It can result in some issues with your vision, however the condition normally clears up without treatment and shouldn’t cause any permanent vision loss.

Types of Optic Neuritis

Optic Neuritis can come in the following types:

Demyelinating Optic Neuritis 

Demyelinating optic neuritis is the most common form of the condition, and it occurs when the myelin coating found on your nerve fibres deteriorates, causing lesions to appear. These can prevent nerve signals from reaching your brain, which can affect your vision.

The cause of demyelination is not fully known; however, some evidence suggests that the breakdown of myelin is a result of the body’s own immune system. Demyelinating optic neuritis may not exhibit any symptoms, however if there are symptoms the condition is called acute demyelinating optic neuritis.

Retrobulbar Optic Neuritis

Retrobulbar optic neuritis is when the inflammation is on the back of the nerve behind the eye, which can make it painful to move your eye around.

Optic Papillitis 

Optic papillitis is when the head of the optic nerve is inflamed.

Signs & Symptoms

Optic neuritis can affect your eyes in different ways, but it may present with one or more of the following symptoms:

• Blurred Vision
• Loss of Vision
• Central Blind Spot
• Poor Colour Vision
• Phosphenes (light flashes when you move your eyes) 
• Pain in your Eye

A version of the condition called acute demyelinating optic neuritis may also present with three characteristic symptoms:

• Your vision may deteriorate significantly in one eye, and can become worse as your body temperature rises from things such as physical exercise, but shouldn’t cause problems in the long term. This is called Uhthoff’s Sign. 
• You may experience pain around your eyes that gets worse when you make movements with your eyes. The pain may appear before your vision deteriorates or it may happen simultaneously.
• Your colour vision may appear reduced or less bright, while some people may also see small flashes of light.

Complications of Optic Neuritis 

The following conditions can arise as a complication caused by optic neuritis:

Optic Atrophy 

Optic neuritis can leave lasting damage to the optic nerve, known as optic atrophy. This can cause permanent changes to your vision such as reduced colour vision, reduced sharpness of vision, or reduced depth and movement perception, while it may also present with no lasting noticeable symptoms.

Repeat Optic Neuritis 

If you have had optic neuritis already, you may be at risk of developing it in your other eye – according to the Optic Neuropathy Treatment Trial (ONTT), 28% of people who had previously had optic neuritis contracted it again within 5 years, and 35% contracted it again after 10 years. While it isn’t certain whether the condition will affect you again, you can talk to your GP or eye care specialist.

Multiple Sclerosis 

There is some evidence that people who contract acute demyelinating optic neuritis may have a 38% risk of developing multiple sclerosis in the next ten years. Multiple sclerosis is a condition that affects the central nervous system, including the brain and spinal cord, and can only be diagnosed by a neurologist. Not all people with acute demyelinating optic neuritis will develop multiple sclerosis in the future, but if you are unsure you can discuss concerns you have with your doctor.

What Causes Optic Neuritis?

Optic neuritis can be caused by your immune system attacking your body (non-infectious), your immune system attacking an infection (parainfectious), or an infection itself (infectious).

Parainfectious Optic Neuritis 

Parainfectious optic neuritis happens as a result of your immune system fighting an infection. It has been connected to conditions such as measles, mumps, rubella, chickenpox, and whooping cough, however immunisation means this can be rare. This type of optic neuritis is more commonly found in children than in adults, and while most people will recover without treatment, severe cases may be treated with a steroid drip.

Infectious Optic Neuritis 

Infectious optic neuritis can occur due to an infection, and the risk of contracting the condition can increase if the infection or any treatment you are given affects your immune system’s ability to work. It is an uncommon form of optic neuritis, and the treatment will depend on the underlying infection.

Non-Infectious Optic Neuritis 

Non-infectious optic neuritis is normally caused by your immune system’s response when there is no infection. It has been linked to a condition known as sarcoidosis, and depending on the severity of your symptoms the treatment can involve steroids to bring inflammation down and an immunosuppressant to weaken your immune system’s response.

Idiopathic Optic Neuritis 

If your eye care specialist is unable to identify the cause of the optic neuritis, they may refer to it as idiopathic optic neuritis. 

How Your Eye Works: The Basics

Four different components work together to form the eye:

The Cornea and Lens – Located at the front of the eye, the cornea and lens act similar to a camera by focusing light onto the retina.
The Retina – Found at the back of the eye, the retina is a layer of cells that receive light and translate it into electrical impulses.
The Optic Nerve – The optic nerve sends the electric impulses to the brain, where they are translated into images.

The Optic Nerve

The optic nerve carries electric impulses from your retina to your brain, and each nerve fibre contains a long segment called an axon. This is coated in myelin, a fatty coating that insulates the axon so it can carry the signals from the retina to the brain without disruption.

When the optic nerve becomes inflamed the signals can become disturbed, meaning your vision would be damaged as signals do not reach the brain properly. 

How is Optic Neuritis Diagnosed? 

Optic neuritis can be diagnosed by your ophthalmologist, who will examine your visual acuity, visual field, and how well you perform on an eye chart. They may also check on your retina and optic discs by pointing a bright light directly in your eyes.

Another test that may be used to diagnose optic neuritis is a Visual Evoked Potentials (VEP) test, where you will look at patterns or moving lights and sensors will measure how active your optic nerve is. VEP tests are only carried out at hospitals. 

You may also be given blood tests to detect any underlying conditions and determine what form of optic neuritis you have, while magnetic resonance imaging (MRI) scans may also be used to get a detailed picture of the insides of your body. 

How do you treat Optic Neuritis? 

Treatment for optic neuritis can involve painkillers to manage any discomfort, but further treatment is not always required as people will normally recover their vision over time.  

When treatment is required, steroids are used in the form of tablets and an intravenous drip. The steroids are initially taken from a drip for three days at the hospital, before tablets are used for two weeks with the dosage reducing on the last three days.

Steroid treatment can speed up the recovery process in severe cases but they don’t generally have any long term benefits. As a result, steroids are rarely used as they can result in side effects at high doses and the benefits are generally not worth the risk. They may be given if the person’s unaffected eye has poor vision, or if vision is essential for the person’s job.