What is Optic Neuritis?
The optic nerve is like an important highway for electrical signals generated in various layers of the retina to leave the eye. These signals start at the photoreceptors (cells in the retina that react to light), get tweaked by specialized retinal cells called bipolar cells, and are then sent through the optic nerves to parts of the brain known as the lateral geniculate bodies. If damage happens to the nerve layer or the optic nerve itself, the quality of these signals can be disrupted.
Optic neuritis (ON) is a term used to encompass different conditions that interfere with the proper functioning of the optic nerve. Many factors can cause such conditions, including infections, injury, poor blood supply, cancer spreading (metastasis), poisons, or deficiencies in vital nutrients. However, this information specifically applies to optic neuritis. This is a condition where the optic nerve gets inflamed, causing the protective coating (myelin) to peel off and, as a result, impacts vision in one or both eyes.
What Causes Optic Neuritis?
Acute optic neuritis (ON), a condition that affects the eye nerve, happens because of a mechanism that’s still uncertain. However, it’s generally believed to be due to an autoimmune reaction. Autoimmune reactions occur when the body’s immune system mistakenly attacks its own cells. In this case, the immune system targets the protective covering of nerve fibers in the optic nerve, known as the myelin sheath, causing damage.
People with confirmed autoimmune diseases are more likely to get optic neuritis. There’s a connection between certain genetic factors (HLA DRB1 and HLA-B27) and ON. Some studies also suggest that ON may occur following viral illnesses, which are known to trigger autoimmune reactions.
Optic neuritis may be a symptom of a disease that causes damage to the nerve fibers in several areas of the brain and spinal cord. This type of disease is known as a demyelinating disease. Often, ON is the first sign of this kind of nerve damage.
Risk Factors and Frequency for Optic Neuritis
Every year, 0.56 to 5.1 out of every 100,000 people develop new cases of optic neuritis (ON). The risk factors include:
- Age, typically between 20 and 40 years
- Sex, with females being twice as likely to develop ON as males
- And race, with Caucasians being more at risk
While kids can get ON in both eyes, it’s rare and it doesn’t necessarily mean they’ll develop multiple sclerosis later. It’s also been suggested that multiple sclerosis is more common in places with mild climates. In fact, studies have found that there are more cases in the northern United States and western Europe than in regions near the equator.
Signs and Symptoms of Optic Neuritis
Optic neuritis is a condition that often starts suddenly in young adults, typically causing pain in one eye and loss of vision. The eye pain often comes with eye movement and might precede vision loss. Some people may experience similar events in the past in the same eye or the other eye.
The vision issues can range from almost normal vision to complete blindness. Any type of visual field defect can occur, but central blind spots are the most common. People may also struggle with color vision (especially red hues) and contrast sensitivity, and may see recurring flashes of light. Interestingly enough, exercise or an increase in body temperature can make the vision loss worse.
One-third of patients will show swelling of the optic disc when their eyes are examined during the active phase of the condition. With no observable inflammation of the optic nerve head, the signs and symptoms are usually enough to diagnose retrobulbar neuritis.
However, if both eyes are affected, if vision loss is severe, or if there was no eye pain before the vision loss, and there are unusual neurologic findings, other potential causes should be considered. Vision generally tends to improve over the course of several weeks to months, with most people regaining near-normal visual function after six months. However, some patients may experience lifelong changes in their vision.
Testing for Optic Neuritis
If your doctor suspects you might have optic neuritis, which is inflammation of the optic nerve that often causes pain and vision loss, they will conduct several tests. These tests may include:
- Checking your best-corrected visual acuity, which is a measure of how well you can see the details of a letter or symbol from a specific distance.
- Performing an automated visual field test to evaluate your entire field of vision.
- Conducting color vision tests, paying special attention to whether the color red seems less vibrant to you. This can be a sign of optic neuritis.
- Examining your pupils to detect a relative afferent pupillary defect (RAPD). This is a condition where the pupils react differently to light, and it can be a sign of optic nerve damage. However, note that this might not always be present if both optic nerves are equally affected.
- Examining your optic nerve, which sends visual information to your brain.
- Using optical coherence tomography (OCT) to assess the health of the retinal nerve fiber layer (RNFL). This is a non-invasive imaging test that uses light waves to take pictures of your retina, the light-sensitive tissue lining the back of your eye.
If these tests suggest you may have optic neuritis, your doctor might order additional testing:
- An MRI scan of your brain and orbits (the cavity in your skull that holds your eye) with and without contrast. This can show areas of demyelination, or damage to the protective covering of nerve fibers. In the active phase of optic neuritis, the affected optic nerve can be seen as enhanced, or brighter, on the scan. If there are demyelinating lesions in your brain, it can confirm a diagnosis of multiple sclerosis, a chronic disorder that affects the central nervous system and often begins with optic neuritis. According to the McDonald criteria, you can be diagnosed with multiple sclerosis after optic neuritis if there are two or more typical lesions, one of which enhances with contrast.
- If your doctor suspects you might have neuromyelitis optica spectrum disorder (NMOSD) – a rare condition that affects the optic nerves and spinal cord – they may order a blood test to detect NMO-IgG antibodies. These proteins can damage critical cells in your brain and spinal cord and are often found in people with NMOSD.
Treatment Options for Optic Neuritis
When struggling with issues that affect your sight, it may be comforting to know that your vision usually improves on its own over time, frequently returning to nearly normal levels within weeks or months. However, treatment with drugs known as corticosteroids can help speed up this recovery.
There’s a well-accepted treatment plan for a condition called optic neuritis (inflammation of the optic nerve that often causes loss of vision or changes in the color you see). This treatment protocol comes from a comprehensive study known as the Optic Neuritis Treatment Trial (ONTT).
According to this plan, corticosteroids are used, first given through an IV (a drip placed in your vein) and then taken orally (by mouth) for a short period. What’s important is that taking these medications orally alone was actually shown to increase the chances of having more optic neuritis issues in the future.
If your doctor uses a special imaging tool called an MRI and sees signs of a disease called multiple sclerosis (characterized by damage to the nervous system), they might consider using immune-modulating therapies. These are treatments designed to alter your body’s immune response to help delay any future attacks on your vision.
What else can Optic Neuritis be?
When it comes to identifying optic neuritis, doctors will consider a range of other potential conditions that may cause similar symptoms. A few of them include:
- Demylelinating diseases such as multiple sclerosis and neuromyelitis optica
- Ischemic optic neuropathy, a condition related to reduced blood flow
- Autoimmune disorders, like systemic lupus erythematosus or giant cell arteritis
- Infectious illnesses including various viral, bacterial, fungal, and parasitic infections
- Reaction to certain drugs, such as ethambutol, amiodarone, or methotrexate
- Nutrient deficiencies, particularly vitamin B12, or toxicity from substances like alcohol or tobacco
- Pressure on the optic nerve due to physical issues within the eye area
The doctor will need to carefully consider all of these when diagnosing optic neuritis, and conduct appropriate tests for an accurate diagnosis.
What to expect with Optic Neuritis
The outlook for people with Optic Neuritis (ON) depends largely on what’s causing it.
In the short term, the discomfort experienced while moving your eyes usually gets better within a few days to weeks. Additionally, vision clarity and color perception typically begin to improve within two weeks to three months. It’s hopeful to note that nearly 90% of patients regain almost normal eye function by six months. Only a small percentage, around 3% of patients, continue to have significant vision issues (20/200 or worse) after 5 years.
In the long term, Optic Neuritis can sometimes be an early sign of more serious diseases. In fact, 15-20% of optic neuritis cases emerge before the onset of Multiple Sclerosis (MS), a disabling disease of the brain and spinal cord. Recurring ON also raises the risk of developing MS or Neuromyelitis Optica Spectrum Disorders (NMOSD) – a group of conditions that cause inflammation and damage to the central nervous system. Around 50% of patients with MS have had at least one attack of optic neuritis in the previous 15 years.
