Optic neuritis is an ocular sign of central nervous system (CNS) inflammation. The CNS is composed of the brain and spinal cord.
Specifically, optic neuritis is inflammation of the optic nerve. Inflammation is the process in the body where white blood vessels and chemical messengers are sent to an area of the body to initiate the healing process or to attack a foreign body. The optic nerve can become inflamed due to autoimmunity, infection, granulomatous diseases, tumor disorders, and demyelination.
The CNS system sends signals from the brain to the other parts of the body through nerves. Nerves tell the parts of the body what to do. Myelin is an insulation that wraps around the axon part of the nerve to speed nerve activity and signal conduction. Myelin is produced by a type of CNS cell called an oligodendrocyte. Attacks of demyelination can occur in parts of the brain, the spinal cord, and the optic nerve.
Who is at risk for developing optic neuritis?
The exact cause and mechanism for developing optic neuritis and MS is unclear but is thought to be a combination of genetic and environmental factors. While anyone can get multiple sclerosis, most cases occur in women, aged 20 to 40, and in the Caucasian and Asian populations. In fact, women are 3x as likely to develop MS, so hormones is thought to play a role. The overall risk is around 1 in 333, according to the National Multiple Sclerosis Society.
MS is not an inherited disease, but 200 genes have been identified that may be small contributing factors to developing the condition, but your chance of developing MS is only slightly higher if a close relative has the condition.
Low vitamin D levels, smoking, migraines, and obesity are other factors. Outdoor activities and diet are recommended for women. Recent study findings indicate bacteria and viruses like a previous Epstein-Barr infection may contribute to the onset of MS.
Geography is also a factor. People who live farther from the equator have a higher risk of developing MS than people who live in warmer areas closer to the equator, or in very cold areas near the north or south poles. Those living beyond the 40-degree mark north or south of the equator are more likely to develop MS.
Surprisingly, a 2021 study demonstrated that hypertension and diabetes are not a contributing factor. However, if you have another autoimmune condition like inflammatory bowel disease or psoriasis, your risk of developing MS is slightly higher. Those with a history of concussions may also be at a higher risk.
How does optic neuritis affect the eye?
Optic neuritis is often a sign of multiple sclerosis (MS) and usually occurs in one eye. If the condition occurs in both eyes, it is unlikely to be MS. The autoimmune condition is associated with vision loss, and pain with eye movement. The vision loss occurs over a few days and stops progressing after one or two weeks. Vision may be blurrier with exercise.
Loss of central vision, dimness in vision, and reduced color vision are also signs. Patients may report more difficulty driving at night due to less contrast and more glare. One in three people will experience flickering lights. The doctor will be able to see an afferent pupillary defect (APD), but the eye usually appears normal on examination. Only one-third of patients will have optic nerve swelling.
It is important for the condition to be identified and treated early. Visual testing may include visual acuity, and color vision. Visual field testing, optical coherence tomography (OCT), an MRI, bloodwork, and spinal fluid analysis may help doctors to make the diagnosis.
Visual field testing will show if there is any loss of the patient’s peripheral vision due to a nerve disorder or problem in the brain. An OCT gives the doctor more information about the nerve fiber layer and the optic nerve head. A diagnosis of MS is made with an MRI. If a patient’s MRI scan shows two or more areas of demyelination in the brain, they are at a higher risk of developing MS.
Multiple sclerosis is called an autoimmune condition because the body attacks itself. Nearly 1 million people are living with MS in the US. Optic neuritis can be the presenting sign of multiple sclerosis in up to 20% of people and occurs in almost half of patients with MS.
Optic neuritis is a demyelinating event of the optic nerve. The eye is considered an extension of the brain. The optic nerve is the doughnut-like structure, located at the back of the eye, that transmits signals from the eye to the brain.
The signals travel through the optic tracts and crisscross at the optic chiasm and then are sent to the brain to interpret the signals. Demyelinating events can also occur behind the optic nerve called retrobulbar optic neuritis. Retrobulbar neuritis is a type of optic neuritis where inflammation occurs somewhere between the back of the nerve and the brain.
Besides ocular symptoms, patients with MS may experience motor symptoms (34.15%), followed by sensory symptoms (24.98%), visual symptoms (21.14%), and brainstem and cerebellar symptoms (19.7%). The most common include numbness and tingling, muscle spasms, stiffness and weakness, mobility problems, and pain.
How is optic neuritis treated?
The diagnosis must be made quickly and treated for the best results. Even without treatment, it may resolve.
Treatment with steroids can speed recovery time and improve one’s vision. Optic neuritis is treated with IV steroids, typically methylprednisone, followed by weeks of oral steroids. Steroids can have effects like GI upset, metallic taste, irritability, and cause an increase in sugar levels. MS medications exist for patients who have areas of demyelination on their MRI scans.
Can you expect your vision to improve?
Your vision is likely to improve although it may not be as good as it was prior to optic neuritis. The degree of improvement will depend upon the cause, the duration and severity of your vision loss, a history of injury, and the success of prior treatments (if any).
A new diagnosis of MS with vision loss from optic neuritis can be very scary for patients. Don’t worry! With diagnosis and treatment, your vision will recover. Today, more than ever before, there are many treatments for MS to control the signs and symptoms.