Optic Neuritis

Risk factors

• Female sex, age 20-45
• White race
• Genetic predisposition to multiple sclerosis (HLA-DR15)
• Higher latitude residence
• Vitamin D deficiency
• Smoking
• Prior viral infection (rare association)

Pathophysiology

Autoimmune inflammation of the optic nerve causes focal demyelination, axonal injury, and edema. Conduction block in demyelinated fibers produces vision loss; resolution of edema and partial remyelination accounts for partial recovery. Aquaporin-4 antibodies (NMOSD) and MOG antibodies (MOGAD) target distinct epitopes and tend to produce more severe, often bilateral, less recoverable disease.

Clinical presentation

Differential diagnosis

• Ischemic optic neuropathy (NAION) — Painless sudden vision loss in patient >50 with vascular risk factors; altitudinal field defect; disc edema with peripapillary hemorrhages; no pain with EOM
• Giant cell arteritis (arteritic AION) — Patient >50 with jaw claudication, headache, scalp tenderness, polymyalgia; ESR/CRP markedly elevated; urgent temporal artery biopsy and IV steroids
• Central retinal artery occlusion — Sudden painless monocular vision loss; cherry-red spot, pale retina, box-carring; ophthalmologic emergency
• Retinal detachment — Photopsias, floaters, curtain of vision loss; dilated exam shows detached retina
• Compressive optic neuropathy (tumor, abscess, thyroid orbitopathy) — Progressive painless vision loss; proptosis, lid retraction, or known mass; MRI reveals lesion
• Toxic/nutritional optic neuropathy — Bilateral, painless, slowly progressive central scotoma; methanol, ethambutol, B12/folate deficiency, alcohol
• Leber hereditary optic neuropathy — Young male, painless sequential bilateral severe central vision loss; mitochondrial inheritance; family history
• Functional/non-organic visual loss — Inconsistent acuity, normal pupils, normal MRI; tunnel vision; diagnosis of exclusion

Diagnostic workup

Diagnostic algorithm

flowchart TD
  A[Acute monocular vision loss<br/>+ pain with eye movement] --> B[Confirm RAPD<br/>+ color desaturation]
  B --> C[MRI brain + orbits<br/>with gadolinium]
  C --> D{Optic nerve<br/>enhancement?}
  D -->|Yes| E[Optic neuritis confirmed]
  E --> F{White matter lesions?<br/>Atypical features?}
  F -->|Typical, unilateral| G[Idiopathic / MS-associated<br/>IV methylprednisolone<br/>1 g x 3-5 d + taper]
  F -->|Bilateral / severe /<br/>poor recovery| H[Test AQP4 + MOG<br/>+ LP for oligoclonal bands]
  H --> I[NMOSD / MOGAD<br/>targeted immunotherapy]
  D -->|No| J[Reconsider:<br/>NAION, GCA, CRAO,<br/>compressive, toxic]

Treatment

Complications

• Persistent visual deficit — most recover to 20/40 or better, but 5-10% have severe permanent loss
• Optic atrophy with reduced contrast sensitivity, color vision, and brightness
• Recurrence — 25-35% over 10 years; more frequent in NMOSD and MOGAD
• Development of multiple sclerosis (high risk when MRI shows white matter lesions)
• Functional impairment, depression, and reduced quality of life

PANCE pearls

• Painful monocular vision loss with RAPD in a young woman is optic neuritis until proven otherwise.
• Color desaturation (especially red) is an early and sensitive sign — test each eye individually.
• Two-thirds of optic neuritis patients have a normal optic disc at presentation — retrobulbar disease.
• MRI brain WITHOUT enhancing lesions reduces but does not eliminate MS risk; consider repeating in 6-12 months in clinically isolated syndrome.
• If bilateral, severe, or with poor recovery, test for AQP4 and MOG antibodies — these change treatment dramatically.
• Always exclude giant cell arteritis in patients older than 50 with vision loss.

References

• AAO PPP — American Academy of Ophthalmology Preferred Practice Pattern: Optic Neuritis (relevant section in Neuro-Ophthalmology PPP)
• ONTT — Optic Neuritis Treatment Trial (Beck et al., NEJM 1992; long-term follow-up Arch Ophthalmol 2008)
• AAN — American Academy of Neurology guidelines on multiple sclerosis disease-modifying therapy and NMOSD diagnostic criteria (Wingerchuk et al., Neurology 2015)