INTRODUCTION — Optic neuritis is an inflammatory, demyelinating condition that causes acute, usually monocular, visual loss. It is highly associated with multiple sclerosis (MS). Optic neuritis is the presenting feature of MS in 15 to 20 percent of patients and occurs in 50 percent at some time during the course of their illness [1-4].
The term optic neuritis is sometimes applied to other inflammatory and infectious conditions affecting the optic nerve. These and other causes of optic neuropathy are discussed separately. (See "Optic neuropathies".)
The epidemiology, pathophysiology, clinical features, and diagnosis of demyelinating optic neuritis will be covered here. Prognosis and treatment of optic neuritis and other clinical manifestations of multiple sclerosis are discussed separately. (See "Optic neuritis: Prognosis and treatment" and "Epidemiology and clinical features of multiple sclerosis in adults" and "Clinically isolated syndromes suggestive of multiple sclerosis".)
EPIDEMIOLOGY — Most cases of acute demyelinating optic neuritis occur in women (two-thirds) and typically develop in patients between the ages of 20 and 40 [5-7].
The incidence of optic neuritis is highest in populations located at higher latitudes, in the northern United States and western Europe, and is lowest in regions closer to the equator. In the United States, studies have estimated the annual incidence of optic neuritis to be as high as 6.4 per 100,000 [8,9]. In the United States, optic neuritis occurs more frequently in whites than blacks [10]. In Asia, optic neuritis is proportionately more common relative to the incidence of multiple sclerosis than in the United States or western Europe [11].
PATHOPHYSIOLOGY — The most common pathologic basis for optic neuritis is inflammatory demyelination of the optic nerve. The pathology is similar to that of acute multiple sclerosis (MS) plaques in the brain, with perivascular cuffing, edema in the myelinated nerve sheaths, and myelin breakdown. Inflammation of the retinal vascular endothelium can precede demyelination and is sometimes visibly manifest as retinal vein sheathing [12]. Myelin loss exceeds axonal loss.
It is believed that the demyelination in optic neuritis is immune-mediated, but the specific mechanism and target antigen(s) are unknown. Systemic T cell activation is identified at symptom onset and precedes changes in the cerebrospinal fluid [13]. Systemic changes also normalize earlier (within two to four weeks) than central changes. T cell activation leads to the release of cytokines and other inflammatory agents. B cell activation against myelin basic protein is not seen in peripheral blood but can be demonstrated in the cerebrospinal fluid of patients with optic neuritis [14].
As with MS, a genetic susceptibility for optic neuritis is suspected. This is supported by an over-representation of certain human leukocyte antigen (HLA) types among patients with optic neuritis [15,16].
CLINICAL FEATURES
Acute features — Optic neuritis is usually monocular in its clinical presentation. In about 10 percent of cases, symptoms occur in both eyes, either simultaneously or in rapid succession [17]. Bilateral optic neuritis is more common in children younger than 12 to 15 years old and also in Asian and black South African patients [17-22]. Because bilateral symptoms are relatively uncommon, they should suggest an alternative cause of optic neuropathy. However, subclinical visual deficits in acuity, contrast sensitivity, color vision, and visual field in the contralateral eye can often be elicited by detailed visual testing in patients with clinically monocular disease [9,23]. Because these deficits usually resolve along with the clinical deficits in the symptomatic eye, it is unlikely that these findings represent prior episodes of optic neuritis.
Other clinical features of optic neuritis were systematically characterized in the Optic Neuritis Treatment Trial (ONTT), which enrolled 457 patients, aged 18 to 46 years, with acute unilateral optic neuritis [7,24]. The two most common symptoms of optic neuritis are vision loss and eye pain:
Other common visual symptoms and signs include:
Chronic features — Even after clinical recovery, signs of optic neuritis can persist. These signs in a patient without a history of optic neuritis may suggest a previous, subclinical attack. When a patient presents with a possible first attack of MS elsewhere in the central nervous system, these signs are often sought because evidence of other demyelinating episodes separated in "time and space" can affect prognosis and treatment decisions. (See "Clinically isolated syndromes suggestive of multiple sclerosis".)
Chronic signs of optic neuritis can include:
DIFFERENTIAL DIAGNOSIS — In a young child, infectious and postinfectious causes of optic nerve impairment should be considered as alternatives to optic neuritis, while in an older patient (>50 years), ischemic optic neuropathy (due, for example, to diabetes mellitus or giant cell arteritis) is a more likely diagnosis than optic neuritis.
The differential diagnosis of optic nerve diseases is summarized in the Tables and is discussed separately (table 1 and table 2). (See "Optic neuropathies".)
DIAGNOSIS — In general, optic neuritis is a clinical diagnosis based upon the history and examination findings. Because important findings on funduscopic examination help differentiate typical from atypical cases of optic neuritis, an ophthalmologic examination should be considered an essential feature of the clinical evaluation.
Diagnostic testing is directed toward excluding other causes of visual loss in atypical cases and in assessing the risk of subsequent multiple sclerosis (MS).
Magnetic resonance imaging — A magnetic resonance imaging study (MRI) of the brain and orbits with gadolinium contrast provides confirmation of the diagnosis of acute demyelinating optic neuritis and important prognostic information regarding the risk of developing MS.
Innovations in MRI technology (eg, short tau inversion recovery [STIR], fast spin echo [FSE], and fluid-attenuated inversion recovery with fat suppression techniques [FLAIR], diffusion tensor imaging [DTI]) have improved imaging of the optic nerve [33-35]. Optic nerve inflammation can be demonstrated in about 95 percent of patients with optic neuritis with gadolinium contrast-enhanced MRI of the brain and orbits (picture 3) [6,36-38]. The longitudinal extent of nerve involvement as seen on MRI correlates with visual impairment at presentation and with visual prognosis [31,36,38]. Gadolinium enhancement persists for a mean of 30 days since onset [31]. The signal abnormality in the nerve can still be seen after recovery of vision, and is also present in as many as 60 percent of patients with MS who do not have a clinical history of optic neuritis [31,39-41].
The brain MRI often shows white matter abnormalities characteristic of MS (picture 4). Typical lesions are ovoid, periventricular, and larger than 3 mm. (See "Diagnosis of multiple sclerosis in adults", section on 'Lesion characteristics'.) The reported prevalence of white matter abnormalities varies substantially among patients with optic neuritis (23 to 75 percent) [42]. In the ONTT, almost 40 percent of patients had MRI lesions, but this trial represents a selected patient group [7]. Small case series of unselected patients have noted a higher coincidence of MRI brain lesions [31,43,44]. Individuals with white matter abnormalities are at a higher risk of developing MS. (See "Optic neuritis: Prognosis and treatment".)
The yield of spinal cord imaging is low in unselected patients. Among 115 patients presenting with optic neuritis, MRI abnormalities in the spinal cord were seen in only four patients with a normal brain MRI [42].
Lumbar puncture — Lumbar puncture is not an essential diagnostic test in optic neuritis, but should be considered in atypical cases (eg, those with bilateral presentation, <15 years in age, or symptoms suggesting infection) [45,46]. Approximately 60 to 80 percent of patients with acute optic neuritis have nonspecific abnormalities in the cerebrospinal fluid (CSF), including lymphocytes (10 to 100) and elevated protein [43].
Other CSF findings in optic neuritis can include [47]:
The presence of OCB implies a higher risk of developing MS. However, since OCB are also associated with white matter lesions on brain MRI, their presence is not clearly of independent prognostic importance [47]. (See "Optic neuritis: Prognosis and treatment".)
Other testing — When there are relevant clues to an alternative diagnosis (table 2), measurement of the erythrocyte sedimentation rate, antinuclear antibodies, and angiotensin converting enzyme levels and serologic and CSF tests for Lyme disease and syphilis should be obtained [45,46]. (See "Optic neuropathies".)
Fluorescein angiography — Fluorescein angiography is not routinely performed in the evaluation of optic neuritis and is often normal. Up to 25 percent demonstrate either dye leakage or perivenous sheathing [12]. These findings may identify patients at somewhat higher risk for developing MS.
Visual evoked response — A delay in the P100 of the visual evoked response (VER) is the electrophysiologic manifestation of slowed conduction in the optic nerve as a result of axonal demyelination [48]. This test is not usually helpful in the diagnosis of acute optic neuritis, unless there is a suspicion that the visual loss is functional.
Abnormalities in the VER can persist after recovery of full vision. At one year, 80 to 90 percent will be abnormal; 35 percent will return to normal at two years [28,31,32]. The VER is often employed to find evidence of previous, asymptomatic, episodes of optic neuritis, but the sensitivity and specificity are imperfect [1].
The multifocal VER is a technical advance that appears to be more sensitive and specific for identifying optic neuritis, but this technology is not generally available [1,49].
Optical coherence tomography — Optical coherence tomography (OCT) measures the thickness in the retinal nerve fiber layer and detects thinning in most (85 percent) of patients with optic neuritis [48,50-53]. Lower values correlate with impaired visual outcome. However, its utility as a prognostic tool is limited in that abnormal values do not show up until early swelling disappears. In one study, OCT was less sensitive than VER in detecting subclinical optic neuritis [54].
A number of studies have found that a greater severity of optic nerve injury seen on OCT suggests neuromyelitis optica rather than optic neuritis associated with multiple sclerosis [55-57].
Aquaporin-4-specific serum autoantibody — Patients with recurrent optic neuritis may be particularly at risk for the variant of MS known as neuromyelitis optica or Devic's disease. This is particularly true for patients with a normal brain MRI and those with optic neuritis events in rapid succession [58]. In one study, seropositivity for the aquaporin-4-specific serum autoantibody was predictive of subsequent NMO among patients with recurrent optic neuritis [59]. This test has been suggested for individuals with recurrent ON, particularly if MRI is negative [60].
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SUMMARY AND RECOMMENDATIONS — Optic neuritis is an acute inflammatory demyelinating injury to the optic nerve.
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