Optic Neuritis – Complete Lecture Notes

 

🎓 Optic Neuritis – Complete Lecture Notes

For Medical Students | Expanded and Structured Clinical Reference

🔍 Definition

Optic neuritis is a neuro-ophthalmologic disorder characterized by acute inflammation and demyelination of the optic nerve, typically presenting with monocular vision loss, pain on eye movement, and impaired color vision. It can be idiopathic or associated with systemic demyelinating disorders such as multiple sclerosis (MS), neuromyelitis optica spectrum disorder (NMOSD), and MOG antibody-associated disease (MOGAD).

📊 Epidemiology & Risk Factors

• Commonly affects females aged 20–45
• Annual incidence: 5 per 100,000 population
• Initial manifestation of MS in 15–20%
• Risk of MS increases if MRI shows white matter lesions
• Higher recurrence in NMOSD and MOGAD patients

🔬 Etiology

• Demyelinating: MS, NMOSD, MOGAD
• Autoimmune: SLE, sarcoidosis, Behçet's disease
• Infectious: Tuberculosis, syphilis, Lyme disease, viral (HSV, VZV, EBV)
• Paraneoplastic syndromes
• Toxic/Nutritional: Methanol, ethambutol, vitamin B12 deficiency
• Hereditary: Leber hereditary optic neuropathy (LHON)

🧠 Pathophysiology

Optic neuritis results from immune-mediated demyelination and inflammation of the optic nerve. This leads to conduction block of nerve impulses along the visual pathway. In MS, autoreactive T cells attack myelin. In NMOSD, anti-aquaporin-4 antibodies target astrocytes. MOGAD involves antibodies against myelin oligodendrocyte glycoprotein. These processes result in axonal damage, neuronal dysfunction, and eventual vision impairment.

🧾 Clinical Presentation

Typically develops over hours to days, often unilateral.

• Visual loss: Sudden or subacute, unilateral
• Pain with eye movement: 90% of cases
• Decreased visual acuity: 6/60 to light perception
• Color vision defects: Especially red desaturation
• Central scotoma
• RAPD: Relative afferent pupillary defect
• Fundus exam: Normal (retrobulbar neuritis) or swollen disc (papillitis)

🧪 Investigations

• MRI Brain & Orbits with contrast: Enhancing optic nerve, white matter lesions suggest MS
• Visual Evoked Potential (VEP): Delayed P100 latency
• OCT (Optical Coherence Tomography): RNFL and ganglion cell complex thinning
• Serum AQP4 and MOG antibodies for NMOSD and MOGAD
• CSF analysis: Oligoclonal bands suggest MS
• Other labs: ANA, ACE, ESR, CRP, VDRL, TB tests

💊 Management & Treatment

Goals: Accelerate recovery, prevent recurrence, identify systemic cause.

• Acute Treatment: IV methylprednisolone 1g/day for 3–5 days
• Oral prednisone: Taper over 11–14 days post-IV therapy
• Immunosuppressive therapy: For NMOSD (rituximab, azathioprine), MOGAD
• MS-modifying agents: Interferon-beta, glatiramer acetate (if MS diagnosed)
• Plasma exchange: In severe or steroid-refractory cases
• Monitoring: Visual fields, VEP, and MRI follow-up

📈 Prognosis

• Vision recovery begins within 1–2 weeks, most recover fully by 4–6 weeks
• Recurrence in MOGAD more frequent than MS
• 50% of optic neuritis patients develop MS in 15 years
• Poor prognostic indicators: Bilateral symptoms, no pain, hemorrhages, persistent visual loss

📌 Differential Diagnosis

• Non-arteritic ischemic optic neuropathy (NAION)
• Compressive optic neuropathy
• Leber hereditary optic neuropathy
• Toxic optic neuropathy
• Uveitis (posterior)

📚 Key References

• Bradley's Neurology in Clinical Practice
• AAO Basic and Clinical Science Course (BCSC) – Neuro-Ophthalmology
• UpToDate – Clinical features and diagnosis of optic neuritis
• Oxford Handbook of Clinical Neurology
• NEJM reviews on MS and optic neuritis

🩺 Prepared for: Meditalk – Supporting Clinical Excellence in Medical Education