What are the diagnostic criteria for confirming optic neuritis?

Diagnostic Confirmation of Optic Neuritis

Optic neuritis is diagnosed clinically through the classic triad of subacute visual loss, periocular pain (especially with eye movement), and dyschromatopsia (red-green color desaturation), supported by objective findings on examination and confirmed with MRI and neurophysiological testing. 1, 2

Clinical Diagnostic Criteria

Essential Clinical Features

• Visual impairment developing subacutely over hours to days 3
• Periocular pain that worsens with eye movement 3, 1
• Red-green color desaturation (dyschromatopsia) 3, 1
• Visual field defects, most commonly central scotomas 1
• Photophobia as a common associated symptom 1

Objective Examination Findings

• Relative afferent pupillary defect (RAPD) in the affected eye in unilateral cases 4
• Optic disc appearance: approximately one-third of patients show mild optic disc edema, while two-thirds have a normal-appearing disc (retrobulbar neuritis) 4
• Clinical documentation of optic nerve atrophy or pallor in chronic cases 3

Confirmatory Diagnostic Testing

MRI Imaging (Primary Diagnostic Tool)

MRI of both orbits and head with contrast is the primary diagnostic study recommended by the American College of Radiology. 5

Key MRI findings include:

• Increased T2 signal within the optic nerve 3, 1
• Gadolinium enhancement of the affected optic nerve 3, 1
• Optic nerve swelling 3, 1
• Coronal fat-suppressed T2-weighted sequences are optimal for visualizing optic nerve lesions 1

Neurophysiological Testing

• Delayed visual evoked potentials (VEPs) confirm optic nerve dysfunction with slowed conduction 3
• VEPs provide objective evidence of optic nerve involvement even when imaging is equivocal 3

Optical Coherence Tomography (OCT)

• Retinal nerve fiber layer (RNFL) thinning provides evidence of optic nerve damage 3
• OCT can document both acute changes and chronic sequelae 3

Red Flags for Atypical Optic Neuritis

Atypical features warrant additional serologic testing for AQP4-IgG and MOG-IgG antibodies to rule out neuromyelitis optica spectrum disorder (NMOSD) and MOG antibody-associated disease (MOGAD). 6, 7

Atypical Features Requiring Further Investigation

• Bilateral simultaneous involvement (suggests NMOSD) 1, 7
• Severe vision loss worse than 20/200 6
• Posterior optic nerve involvement including the chiasm (suggests AQP4-IgG-seropositive NMOSD) 1
• Long optic nerve lesions (suggests NMOSD or MOGAD) 1
• Poor recovery with steroids or steroid dependence 7
• Prominent optic disc edema 7
• Childhood or late adult onset 7
• Non-Caucasian male with optic disc swelling 6

Prognostic Indicators

Brain MRI for Multiple Sclerosis Risk Assessment

• Even one clinically silent T2 hyperintense brain lesion in patients with optic neuritis is highly associated with eventual MS diagnosis 3, 1
• Absence of brain lesions strongly predicts a monophasic illness 3
• CSF oligoclonal bands combined with brain MRI lesions dramatically reduce the likelihood of monophasic illness (HR 5.1 for 1-3 lesions, HR 11.3 for ≥10 lesions) 3

Common Pitfalls to Avoid

• Do not rely on oral history alone—objective documentation of RAPD, color vision deficits, and visual field defects is essential 2, 4
• Do not assume bilateral presentation is typical—this is a red flag for NMOSD or MOGAD requiring antibody testing 1, 7
• Do not skip brain MRI—it is critical for MS risk stratification even in isolated optic neuritis 3, 1
• Do not confuse with anterior ischemic optic neuropathy (AION)—AION typically lacks pain and occurs in older patients with vascular risk factors 2