Chances are, you’ll have a patient present to your office with decreased vision and/or a swollen optic nerve at some point in your career as an optometrist. Whether the swollen nerve is secondary to a brain tumor, ischemic optic neuropathy, or optic neuritis, it’s important to be able to recognize the signs, symptoms, and characteristics of patients with each condition. This piece will focus on optic neuritis specifically, as the incidence in the United States is estimated to be as high as 6.4 cases per 100,000 people. Here’s what you need to know about optic neuritis, how to properly treat the condition, and how to inform your patients about their options.
What is optic neuritis?
Optic neuritis is an acute inflammatory demyelinating disorder of the optic nerve. When we as optometrists hear the term optic neuritis, we usually think of a middle-aged female because of the condition’s association with multiple sclerosis. This makes sense, as optic neuritis most often occurs in individuals ages 20-50, and is three times more likely to affect females. This statistic mirrors the prevalence of multiple sclerosis.
Optic neuritis is also more common in higher latitudes, such as the northern United States and Western Europe, and is less common in regions closer to the equator. Optic neuritis is much more common in Caucasians. Knowing the demographics is important, given that you likely see patients from many backgrounds and races.
How would patients with optic neuritis present to your clinic, you might ask?
Diagnosing optic neuritis
I’ve noticed from my time in practice that the severity of symptoms varies widely in those with optic neuritis. The majority of these patients have blurred vision, periorbital pain that worsens with eye movement, color vision loss, and visual field defects. Patients with optic neuritis also commonly present with a relative afferent pupillary defect in the affected eye. Their vision loss is typically monocular and progresses up to one week from the onset of the condition.
In the Optic Neuritis Treatment Trial (ONTT), vision ranged from 20/50 to 20/200 with an average acuity of 20/60. Furthermore, 11% of patients in the study had 20/20 acuity and 3% had no light perception. The ONTT also showed that vision tends to improve within four to 12 weeks, while painful eye movement resolves within two weeks. Patterns of visual field loss vary, but are commonly seen as arcuate, altitudinal, or central. This is important because it shows that acuity and field loss can vary greatly. It is essential for you to keep an open mind and to remember that clinical presentations don’t always have to be “textbook.”
Classification and causes
Optic neuritis is classified both by how the optic nerve appears and by what causes it. Appearance-wise, optic neuritis is classified into three categories.
Causes of optic neuritis are broken down into idiopathic, demyelinating, parainfective, and infective etiologies.
Demyelinating causes include multiple sclerosis and neuromyelitis optica. Multiple sclerosis-related optic neuritis is thought to be immune-mediated, with systemic T cells crossing the blood-brain barrier leading to the release of cytokines and other inflammatory mediators. This inflammatory response causes swelling of the myelinated nerve sheath with resultant myelin breakdown and axonal loss.
Neuromyelitis optica (NMO) is sometimes mistakenly thought to be a continuum or subset of MS, but it’s a different clinical entity. NMO is a central nervous system disorder caused by autoantibodies against plasma membrane water channels. This primarily causes inflammation of the spinal cord and optic nerve. Isolated optic neuritis is a common presenting sign in both MS and NMO. While both MS and NMO are autoimmune, they differ in a few ways. There is a blood test which can help with the diagnosis of NMO, called the NMO-IgG blood test. Seventy percent of patients with NMO have a positive blood test. On the other hand, there is no blood test to help diagnose MS. Patients with NMO usually have severe vision loss, while most MS patients recover significant vision after an episode of optic neuritis.
Parainfective causes of optic neuritis include childhood infections such as chickenpox, rubella, mumps, and measles while infective causes include cat-scratch fever, syphilis, sinusitis, tuberculosis, sarcoidosis, and Lyme disease.
If optic neuritis is infectious in nature, patients will likely have systemic symptoms such as malaise, fever, weight loss, hair loss, coughing, chills, night sweats, body rashes, and lymphadenopathy. Examples of blood tests that can be done to rule out these infectious causes include RPR/VDRL/FTA-ABS for syphilis, ACE for sarcoidosis, IGRA for tuberculosis, and IgM/IgG antibodies for cat-scratch disease.
Optic neuritis and multiple sclerosis
If your patient presents with signs and symptoms of optic neuritis and they tell you they’ve had recent episodes of blurred vision after exercising, you should be thinking about multiple sclerosis (MS). This is referred to as Uhthoff’s phenomenon and may also occur with NMO, although it’s less common. Over 50% of patients with MS will develop optic neuritis at some point during their lives. Optic neuritis is the presenting feature of MS in about 20% of patients. Referring to neuro-ophthalmology for management is appropriate as imaging and further testing may be needed.
If a patient has a known diagnosis of MS with a classic case of optic neuritis, no further testing may be indicated. However, since optic neuritis may occur before someone is officially diagnosed with MS, it’s important to order a magnetic resonance image (MRI) of the brain and orbits. MRI is used to look for characteristic white matter lesions and is also used to monitor disease progression.
Bear in mind that, according to research, a normal MRI does not necessarily rule out MS, since about 5% of patients with MS don't show white matter lesions. If one of your optic neuritis patients has a normal MRI, they have a 15% chance of developing MS after five years and a 25% chance after 15 years. If their MRI shows white matter lesions, their risk is significantly higher at 50% after five years and 70% after 15 years. Some clinical characteristics which make MS or NMO highly unlikely include no white matter lesions on MRI, no light perception vision, severe disc swelling, no eye pain, retinal exudates, and peripapillary hemorrhages.
Optic neuritis treatment
So, you might be thinking “what can be done for my patients?” Thanks to the Optic Neuritis Treatment Trial, we know that high-dose intravenous methylprednisolone leads to faster visual recovery, however, it does not improve final visual acuity, visual field defects, or color vision perception. In fact, high-dose IV steroids were no more effective than oral prednisolone or placebo. Low-dose oral steroids are contraindicated for patients with optic neuritis, as patients who were treated with oral prednisolone alone in the treatment trial were twice as likely to have recurrences within six months. Patients treated with high-dose IV steroids had fewer relapses of MS in the following two years than those treated with low-dose oral steroids. If optic neuritis is found to be secondary to neuromyelitis optica, it requires more intense and longer steroid treatment.
Patients who are deemed “high risk” for developing MS based on their MRI findings are treated prophylactically with newer oral medications and sometimes older injectable medications. These medications are approved for the treatment of MS and have been shown to lessen the number of new white matter lesions and slow progression of neurologic impairment.
Whether optic neuritis is caused by MS or cat-scratch disease, it is important for us as optometrists to be able to recognize its characteristics and to know the clinical course of the most common etiologies. We should encourage our patients to remain positive and counsel them on their potential for regaining vision after their case of optic neuritis resolves. Especially in the case of MS, but with all optic neuritis patients, it’s crucial to act fast and take proper measures. Speedy evaluation and referral to neurology may make a large impact on the patient and their future quality of life.
Photo 1: Link
Photo 2: Link
Photo 3: Patient I had from my year of residency at the Salisbury VAMC. I used this photo in my final VA residency presentation.