Jane W. Chan, MD–Associate Professor of Neurology Ophthalmology, Departments of Neurology and Ophthalmology, University of Kentucky Medical Center, Lexington, Kentucky
Risk Factors for Developing Optic Neuritis in Autoimmune Disease
Although optic neuritis most often affects young adults, atypical cases of optic neuritis are sometimes seen in elderly patients. Bilateral optic neuritis in childhood is not uncommon, and it is believed that in these cases there is less risk of progression to MS (Beck et al., 1993b).
SEX: Women are twice as likely as men are to develop optic neuritis (Beck et al., 1993b)
RACE: Optic neuritis occurs more frequently in Caucasians than in other races (Beck et al., 1993b)
GENETICS: Certain genetic mutations may increase your risk of developing optic neuritis or multiple sclerosis (Hauser et al., 2000).
The Optic Nerve
When light hits the retina, electrical impulses are generated and carried along the optic nerve to your brain, where the impulses are converted into visual information. The optic nerve is covered by fatty, insulating material called myelin, which helps electrical impulses travel quickly along the nerve. Swelling and destruction of this myelin sheath impairs conduction of nerve impulses along the optic nerve. Direct axonal damage may also play a role in nerve destruction itself (Chan, 2002).
Optic neuritis usually affects young women ranging from 18-45 years of age, with a mean age of 30-35 years. The annual incidence is approximately 5/100,000, with a prevalence estimated to be 115/100,000 (Kantarci & Wingerchuk, 2006).
Different Causes of Optic Neuritis
Optic neuritis is a demyelinating (the loss of nerve fiber ‘insulation’ from disease processes which impairs conduction of nerve impulses along the nerve) inflammation of the optic nerve. It is commonly associated with multiple sclerosis (MS) but can occur in isolation. In MS, optic neuritis is often the first manifestation of the disease. Long-term follow-up studies have indicated that up to 75% of women initially presenting with optic neuritis eventually develop MS (Chan, 2002).
MS is a disease in which your autoimmune system attacks the myelin sheath covering nerve fibers in your brain and spinal cord. Another autoimmune disorder that may cause optic neuritis is neuromyelitis optica (NMO), where demyelination usually affects the optic nerve and the spinal cord, and involves the brain less often than in MS. Optic neuritis related to NMO is often more severe than optic neuritis associated with MS. Visual recovery is poor in NMO, whereas it is good in MS (Wingerchuk, Lennon, Lucchinetti, Pittock, & Weinshenker, 2006; 2007).
Although optic neuritis is often related to MS or other demyelinating disorders, such as NMO, demyelination is not the only cause for optic neuritis. Bacterial infections, including Lyme disease, cat scratch fever and syphilis, or viruses such as HIV, hepatitis B, and herpes can cause optic neuritis. Other autoimmune disorders, such as lupus and temporal arteritis, can cause vasculitis, which is inflammation of the blood vessels supplying blood to the optic nerve, resulting in anterior ischemic optic neuropathy that is like a stroke to the optic nerve. Even some medications, such as ethambutol, used to treat tuberculosis, can occasionally cause optic nerve swelling. Chronic optic disc swelling can sometimes be a complication of diabetes. Other causes include tumors, nutritional deficiencies, and various toxins (Chan, 2002).
Risk of Developing MS After Optic Neuritis
After 2 years from the onset of optic neuritis, among patients who participated in the Optic Neuritis Treatment Trial (ONTT), those with an abnormal MRI of the brain (white matter lesions), had a 36% risk of developing another symptom or sign of MS within 2 years. Only 3% of patients in that study with a normal MRI of the brain, however, had another symptom or sign of MS within 2 years (Beck & Trobe, 1995).
On the other hand, having optic neuritis and a normal MRI of the brain only increased the risk by 22%. Based on the 15-year data from the ONTT, approximately 75% of women developed MS, and about 34% of men developed MS (Beck et al., 2003).
Symptoms and Signs of Optic Neuritis
Optic neuritis usually affects one eye, but it may occasionally occur in both eyes simultaneously (Cleary, Beck, Bourque, Backlund, & Miskala, 1997).
Eye Pain: Eye pain that worsens with eye movement is a common feature of optic neuritis. Pain associated with optic neuritis usually peaks within one week and then goes away in several days. A study found that 92.2% of patients experienced pain, which actually preceded the visual loss in 39.5% of cases (Cleary et al, 1997).
Visual Loss: The extent of visual loss associated with optic neuritis varies. It can range from severe difficulty in seeing, such as blurred or foggy vision, to barely noticeable changes in vision. Visual loss may be worsened by heat or exercise (Uthoff’s phenomenon). Vision loss is usually transient and may worsen over a period of approximately 7 days, then typically remains at that level for 3 to 8 weeks, followed by gradual visual improvement. But in rare cases, it may be permanent. Most people with optic neuritis will recover much of their vision within 6 months from the onset of visual loss (Cleary et al., 1997).
Loss of Color Vision: Optic neuritis often affects the perception of colors. Red colors temporarily appear dull or less bright than normal in the affected eye. Distinguishing red and green colors is usually difficult on color vision testing (Cleary et al., 1997).
Eye Examination for Optic Neuritis
Visual acuity testing: This test measures the ability to identify black symbols on a white background at a standardized distance as the size of the symbols is varied. Visual acuity represents the smallest size that can be reliably identified. The phrase â€œ20-20 visionâ€ refers to the distance in feet that objects separated by an angle of 1 arc minute can be distinguished as separate objects. (Keltner, Johnson, Spurr, & Beck, 1994; 1999).
Visual field testing: Perimetry is the systematic measurement of differential light sensitivity in the visual field (extent of the observable world that is seen at any given moment) by the detection of test targets on a background. The extent of the visual field can be quantitatively determined by a computerized program in which the test taker gazes at a central target and pushes a button whenever a light is detected in the peripheral field of vision. Optic neuritis can cause a variety of visual field abnormalities, such as a â€œspotâ€ in the center of vision or a dark area in the peripheral vision (Chan, 2002).
Color testing: A book of color plates may be used to test for abnormal color vision. Optic neuritis often causes difficulty in recognizing red and green colors (Chan, 2002).
Pupillary light reaction test: To see how pupils respond when they are exposed to bright light, a light is shown into each eye. Eyes affected by optic neuritis do not constrict as well as normal eyes do when stimulated by light (Chan, 2002).
Ophthalmoscopy: After dilating the eyes with eye drops, an ophthalmoscope is used to examine the optic disc, which is the structure where the optic nerve enters the retina in your eye. The optic disc usually appears normal because most of the swelling is located behind the eye. In about 1/3 of cases, it may be swollen (Chan, 2002).
Other Tests to Help Diagnose Optic Neuritis and MS
Visual evoked potentials (VEP) testing: An alternating checkerboard pattern is displayed on a monitor screen while wires on small patches attached to the scalp record the brain’s responses to the visual stimulation. This test measures the delay in electrical conduction resulting from inflammation and/or axonal damage of your optic nerves. The VEP helps confirm the diagnosis of optic neuritis, especially when the MRI scan of the brain and orbits appears normal. It can also detect previous optic nerve damage when no apparent visual symptoms or signs of optic neuritis are present (Chan, 2002).
Magnetic resonance imaging (MRI) scan:An MRI is a radiologic test that uses a magnetic field and pulses of radio wave energy to produce images of the body. A contrast agent is injected into the vein so that the optic nerve and other parts of the brain become more visible on the images. MRI is a highly sensitive and specific tool in assessing inflammatory changes in the optic nerves. This scan will also determine whether demyelinated areas are present in the brain and can help rule out tumors or other conditions that can mimic optic neuritis.
MRI can help predict future development of MS in patients presenting with first-time acute optic neuritis. In 10 to 20% of MRIs performed at initial presentation of optic neuritis, clinically silent demyelinative lesions were seen elsewhere in the brain. Persons with clinically silent MS lesions were found to be more likely to develop definite MS in the long-term than those with isolated optic neuritis without any brain MS lesions. The ONTT reported the 10-year risk of MS to be 56% with at least one MRI lesion (Beck, Arrington, Murtagh, Cleary & Kaufman, 1993).
Blood tests: Several blood tests, such as erythrocyte sedimentation rate, thyroid function tests, antinuclear antibodies, angiotensin-converting enzyme, rapid plasma regain (RPR), and mitochondrial DNA mutation studies may be used to exclude causes of optic neuropathy other than demyelinating optic neuritis. If optic neuritis is severe, an NMO-IgG blood test can check for neuromyelitis optica antibodies. This test helps to confirm the diagnosis of neuromyelitis optica, but a negative test result does not rule out the possibility of not having this disorder (Weinshenker, Wingerchuk, Pittock, Lucchinetti, & Lennon, 2006).
Spinal tap: A spinal tap is a procedure that collects cerebrospinal fluid (CSF) from your lower back area under local anesthesia. CSF analysis can show the presence of MS-related proteins, such as myelin basic protein, oligoclonal bands, and elevated IgG index and synthesis rate, to support the diagnosis of MS. Even in the absence of other clinical signs of MS during the initial presentation, patients with abnormal CSF findings suggestive of demyelination are more likely to develop MS in the long term (Cole, Beck, Moke, Kaufman & Tourtellotte, 1998; Rolak et al., 1996).
Recovery from Optic Neuritis
The prognosis following optic neuritis is generally good. Most people regain normal vision 2 months, and as long as 6 months, after an episode of optic neuritis. People with MS or neuromyelitis optica, however, may experience recurrent attacks of optic neuritis after they have recovered from the initial episode. Other people without any underlying conditions also may have recurrent optic neuritis; these people have a better prognosis for their vision in the long term than do people with neuromyelitis optica (Beck, Cleary, & Backlund, 1994; Beck & Cleary, 1993).
The affected optic nerve becomes pale after optic neuritis and the affected pupil may not react as well to light. Although visual acuity returns close to normal, residual visual symptoms can persist. About 20 percent of people with optic neuritis can have some degree of long-term vision loss. Some people may experience decreased contrast sensitivity, defective color vision, subtle visual field defects, and reduced brightness sensitivity. Some practical strategies in dealing with these visual problems will be outlined in the next section (Beck et al., 1994; Beck et al., 1993).
Treatment of Optic Neuritis
Acute Treatment of Optic Neuritis
Optic neuritis usually gets better on its own. Corticosteroids help reduce inflammation in the optic nerve to reduce ocular pain and discomfort. This treatment can also help you recover your vision faster, but it doesnâ€™t appear to affect the extent to which you will recover your vision. Intravenous corticosteroids have also been found to reduce the risk of developing MS in the following 2-year period in those patients who have MRI lesions (Beck et al., 1993).
Corticosteroid therapy is administered by vein (intravenously) for 3 days. After intravenous therapy, an oral prednisone taper is given for several weeks (Beck et al., 1993a; 1993b).
Long-term Prevention of MS Progression
People who have optic neuritis and are at high risk of developing MS may benefit from interferon beta-1a (AvonexÂ®, RebifÂ®) and interferon beta-1b (BetaseronÂ®). These injectable drugs are used to prevent or delay the development of MS in people with optic neuritis who have two or more brain lesions evident on MRI scans (Beck et al., 2002; Jacobs et al., 2000).
Management of Low Vision Associated With Optic Neuritis
Improvement of vision can be accomplished by changing the following aspects of the environment:
-Contrast is the difference between lightness and darkness of colors. Paint or colored tape can be used to mark light switches, doorways, or steps.
-The intensity of lighting can be increased with incandescent and halogen bulbs. Fluorescent lights can cause glare. Light should be aimed directly where it is needed. Low-level lighting or diffuse lighting should be avoided. Wearing graytinted sunglasses for outdoors can help eliminate glare.
-Texture defines the edges and the outlines of objects. Masking tape or VelcroÂ® tape can be used to help define commonly used objects, such as light switches and buttons.
For more specific needs, a low vision specialist can prescribe an optical device, such as a microscopic or telescopic eyewear, a magnifier, or a closed-circuit TV magnifier on screen. Low Vision Gateway www.lowvision.org has a list of computer software programs that can modify the computer for larger fonts and images (Lampert & Lapolice, 1995). The following organizations can also offer further assistance:
-American Foundation for the Blind-www.afb.org
-American Printing House for the Blind-www.aph.org
-Low Vision Information Center-www.lowvisioninfo.org
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