Optic neuritis

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Optic neuritis is inflammation of the optic nerve rather than one disease. Typical optic neuritis often accompanies multiple sclerosis, while neuromyelitis optica spectrum disorder, MOG-antibody-associated disease, infection, sarcoidosis and systemic autoimmunity produce overlapping but clinically important patterns. 'Optic neuritis' should therefore be followed by a phenotype—side, severity, disc appearance, segment length, associated myelitis or brain syndrome—and not treated as synonymous with MS.

The afferent visual pathway is examined one eye at a time. Acuity measures central resolution; colour plates or red desaturation probe colour function; fields map axonal distribution; the swinging-flashlight test compares afferent input; fundoscopy evaluates disc and retina. Pain and colour loss out of proportion to acuity can support neuritis. Optical coherence tomography measures retinal nerve-fibre and ganglion-cell layers but structural thinning develops after axonal injury and does not replace acute clinical assessment.

Typical demyelinating neuritis is generally unilateral, moderate and painful, with spontaneous improvement. Atypical flags include age extremes, no pain, severe acuity loss, bilateral simultaneous disease, prominent disc oedema or haemorrhage, retinal inflammation, chiasmal involvement, encephalopathy, recurrent same-eye attacks and poor recovery. These features prompt urgent testing for antibody-mediated, infectious, granulomatous, infiltrative, compressive and ischaemic causes.

Multiple-sclerosis risk depends on clinical history and MRI lesion pattern, not optic neuritis alone. The first episode may be a clinically isolated syndrome. Neurology applies current diagnostic criteria and discusses disease-modifying therapy when appropriate. Treatment of the acute visual attack is individualised: many typical cases recover well without steroids, whereas severe or antibody-associated attacks may need high-dose corticosteroid and escalation such as plasma exchange under specialist protocols.

Key points

Typical demyelinating optic neuritis usually causes subacute monocular visual loss over hours to days, pain worsened by eye movement, reduced colour saturation, a central or caecocentral field defect and a relative afferent pupillary defect.
The optic disc is often normal because inflammation is retrobulbar. A normal-looking disc does not exclude substantial optic-nerve dysfunction; marked swelling, haemorrhage or exudate is atypical and broadens the differential.
Measure corrected acuity in each eye, red or colour perception, pupils, confrontation fields and fundi. A binocular acuity result or vague statement that vision is blurred cannot localise the lesion.
Pain with eye movement supports optic neuritis but is not specific; sinus, orbital and ocular inflammatory disease can cause pain, while some demyelinating and antibody-associated neuritis is painless.
A relative afferent pupillary defect is expected in unilateral or asymmetric optic neuropathy. It may be absent when disease is bilaterally symmetric and does not arise from refractive error alone.
Typical recovery begins within weeks. Progressive loss beyond roughly two weeks, absence of early recovery, recurrence in the same nerve, severe bilateral disease or steroid-dependent relapse is atypical.
Younger age and painful central visual loss favour demyelinating neuritis; sudden painless altitudinal loss with a swollen disc in an older vascular-risk patient favours anterior ischaemic optic neuropathy.
Ask about previous neurological episodes, myelitis, persistent vomiting or hiccups, autoimmune disease, infection, medicines, nutritional and toxic exposure, cancer, headache, jaw claudication and polymyalgic symptoms.
MRI of brain and orbits with dedicated fat-suppressed post-contrast optic-nerve sequences supports the diagnosis, identifies lesions suggesting multiple sclerosis and helps characterise long or chiasmal inflammation.
Aquaporin-4 and MOG antibody testing is reserved for phenotypes such as bilateral, severe, recurrent, longitudinally extensive, chiasmal or markedly swollen neuritis and is interpreted by neuroimmunology specialists.
High-dose corticosteroid can hasten recovery in selected demyelinating attacks but does not justify low-dose oral steroid treatment, which is not a substitute for correct diagnosis and may be inappropriate in infection.
Provide driving, work and safety advice based on current acuity and fields, and ensure both final visual outcome and the risk of future demyelinating events are reviewed.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Multiple-sclerosis-associated inflammation

Typical painful unilateral optic neuritis often represents a first or established MS demyelinating attack, particularly when brain MRI shows characteristic lesions.

MOG-associated disease

MOG antibodies commonly accompany bilateral, recurrent or markedly swollen optic neuritis and can produce extensive anterior nerve involvement.

Aquaporin-four NMOSD

AQP4 autoimmunity causes severe, often posterior, chiasmal or bilateral optic neuritis with high risk of incomplete recovery.

Infectious and systemic inflammation

Sarcoid, vasculitis, infection and other immune disease can inflame the optic nerve, especially when pain, imaging or systemic features are atypical.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Optic-nerve inflammation
Immune cells and antibodies disrupt the blood–nerve barrier and create focal or extensive inflammation within the optic nerve.
2
Demyelination and oedema
Myelin injury and swelling slow or block retinal ganglion-cell axons, reducing acuity, colour perception and visual-field transmission.
3
Axonal degeneration
Severe or prolonged inflammation damages axons, causing retinal nerve-fibre loss, optic atrophy and fixed visual impairment.
4
Remyelination and adaptation
Resolution of oedema and partial remyelination permit recovery over weeks, although contrast and colour deficits may remain.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Typical demyelinating optic neuritisRed flag

Subacute unilateral central visual loss, dyschromatopsia, eye-movement pain and a relative afferent pupil defect with a normal or mildly swollen disc in a younger adult supports typical optic neuritis.

MOG-associated patternRed flag

Severe optic-disc swelling, bilateral or recurrent attacks, long anterior optic-nerve enhancement and good steroid responsiveness with relapse on withdrawal can suggest MOG-antibody-associated disease.

Aquaporin-4 associated patternRed flag

Profound visual loss, posterior or chiasmal involvement, poor spontaneous recovery and associated longitudinally extensive myelitis or area-postrema symptoms raises neuromyelitis optica spectrum disorder.

Anterior ischaemic optic neuropathyRed flag

Sudden painless monocular loss, often altitudinal, with a swollen disc in an older adult suggests ischaemic rather than inflammatory optic neuropathy; giant-cell-arteritis symptoms make treatment an immediate emergency.

Compressive optic neuropathyRed flag

Progressive painless loss, optic pallor, proptosis, dysmotility, asymmetrical disc change or a junctional field pattern suggests orbital, canalicular or chiasmal compression and needs targeted imaging.

Toxic or nutritional neuropathy

Usually symmetric, painless, slowly progressive central or caecocentral loss with colour impairment suggests toxic or nutritional disease; medication, alcohol, diet, bariatric and nitrous-oxide histories are essential.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Corrected acuity, colour, pupil and visual-field examinationFirst step
Why
Confirm objective afferent dysfunction, quantify severity and provide a baseline for recovery.
Interpretation and limitations
Test each eye separately with correction and record chart and distance. Relative afferent defects identify asymmetry, while formal perimetry defines central, altitudinal or chiasmal patterns more reliably than confrontation.
02
Dilated fundus and ocular examination
Why
Differentiate retrobulbar neuritis from disc, retinal, vascular, inflammatory and pressure-related eye disease.
Interpretation and limitations
A normal disc is compatible with retrobulbar neuritis. Disc haemorrhage, macular or retinal pathology, severe swelling or uveitis is atypical and should redirect investigation.
03
MRI brain and orbits with contrast
Why
Demonstrate optic-nerve inflammation, map segment and chiasm involvement and assess brain lesions relevant to demyelinating diagnosis and prognosis.
Interpretation and limitations
Request dedicated thin fat-suppressed orbital sequences; a routine brain MRI can miss optic-nerve enhancement. Enhancement supports inflammation but is not unique to one antibody disorder.
04
Optical coherence tomography
Why
Measure optic-disc swelling and retinal nerve-fibre or ganglion-cell loss and provide a reproducible structural baseline.
Interpretation and limitations
Acute oedema can thicken the nerve-fibre layer and mask loss; ganglion-cell and later nerve-fibre thinning reflect injury but do not determine aetiology alone.
05
Aquaporin-4 and MOG-IgG assays
Why
Identify antibody-associated disease when severity, bilaterality, recurrence, MRI pattern or associated myelitis makes it plausible.
Interpretation and limitations
Use validated cell-based assays and specialist interpretation. Low-level or isolated results can mislead when pre-test probability is low, and recent immune treatment can affect sampling.
06
ESR, CRP, FBC and targeted infectious or inflammatory tests
Why
Assess giant-cell arteritis and selected systemic, granulomatous, infectious, nutritional or toxic alternatives.
Interpretation and limitations
Age, disc appearance, systemic symptoms and exposure guide testing. Normal inflammatory markers reduce but do not absolutely exclude giant-cell arteritis when the phenotype is strongly suspicious.
07
Lumbar puncture with paired oligoclonal bands
Why
Support a demyelinating or inflammatory diagnosis when MRI and clinical criteria leave an important uncertainty.
Interpretation and limitations
CSF-restricted bands are not specific to MS and puncture is not obligatory in every typical optic neuritis. Obtain paired serum and apply current criteria through neurology.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Anterior ischaemic optic neuropathy

Sudden painless altitudinal loss with disc swelling in an older vascular-risk person favours ischaemic injury over typical demyelinating neuritis.

Compressive optic neuropathy

Slow progression, proptosis, persistent disc pallor or a mass along the optic pathway supports tumour, aneurysm or orbital compression.

Infectious or infiltrative neuropathy

Fever, immune suppression, marked cerebrospinal-fluid change, systemic inflammation or persistent enhancement suggests infection, sarcoid or malignancy.

Retinal disease

Retinal haemorrhage, exudate, detachment or macular findings explain visual loss without the characteristic afferent pupil and optic-nerve pattern.

Additional chapter-specific clues

Retinal mimicRed flag

Photopsia, metamorphopsia, retinal whitening, haemorrhage, vascular occlusion or detachment signs point to retina rather than optic nerve. A relative afferent defect can occur in severe asymmetric retinal disease.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Acute monocular lossLocalise before assuming neuritisFirst stepVision declines over minutes to days with pain, colour change, field loss or an afferent pupil defect.

1Obtain exact onset and systemic symptoms and perform corrected monocular acuity, colour, fields, pupils, fundi and a complete neurological and ocular-motor examination.
2Arrange same-day ophthalmic or neuro-ophthalmic assessment to exclude retinal vascular, giant-cell-arteritis, pressure and structural emergencies, sending ESR, CRP and platelets immediately when arteritis is possible.
3Use dedicated MRI brain and orbits and specialist-selected serology or CSF to phenotype inflammation, then agree whether observation, high-dose steroid or another urgent treatment is appropriate.

02Atypical severe neuritisEscalate antibody and infectious evaluationEscalationVisual loss is bilateral, profound, recurrent, chiasmal, markedly swollen, painless or associated with myelitis, systemic inflammation or poor recovery.

1Admit or arrange urgent neuro-ophthalmic and neuroimmunology review according to severity, documenting both eyes, neurological level, bladder function and systemic or infectious clues.
2Obtain protocolled MRI of orbits, brain and cord as indicated and send AQP4-IgG, MOG-IgG and targeted infection or systemic tests before immune treatment where this does not cause harmful delay.
3EscalationStart and escalate immunotherapy only through the specialist pathway, monitoring vision closely and reconsidering infection, compression or ischaemia when response is atypical.

03Typical demyelinating attackSupport recovery and assess future riskAlternativeA specialist confirms a conventional unilateral demyelinating optic neuritis without an immediate alternative emergency.

1Discuss likely natural recovery and the benefit and limitations of high-dose corticosteroid, considering functional severity, diabetes, psychiatric risk, pregnancy, infection and patient preference.
2Arrange neurology review of brain MRI and prior episodes using the 2024 revised McDonald criteria, recognising that objective optic-nerve involvement can supply the fifth anatomical location; do not diagnose MS from optic neuritis alone without the full criteria and exclusion of mimics.
3Follow acuity, colour and fields to objective recovery and address driving, work, heat-related symptom fluctuation and return for new visual, cord or brainstem symptoms.

Key medicines and prescribing safety1 treatment · regimens, roles and cautions

Can accelerate visual recovery from a functionally important inflammatory attack but does not by itself establish the cause or guarantee better final acuity.

High-dose methylprednisolone for selected demyelinating relapse

When a neurologist or neuro-ophthalmologist recommends relapse treatment, use oral methylprednisolone 500 mg daily for five days, or intravenous methylprednisolone 1 g daily for three to five days when the NICE alternative criteria apply.

Exclude or treat important infection and review diabetes, mood or psychosis, gastrointestinal, blood-pressure and pregnancy risks; do not use lower-dose steroid regimens for MS relapse or start repeated courses without specialist reassessment.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Permanent visual impairment

Axonal loss can leave reduced acuity, colour, contrast and fields, affecting driving, reading and employment after severe attacks.

Future demyelinating disease

A first typical attack may precede multiple sclerosis, while antibody-positive disease carries distinct relapse and disability risks.

Bilateral or recurrent blindness

AQP4 and some MOG phenotypes can repeatedly injure both nerves, making early attack and relapse-prevention decisions consequential.

Treatment and diagnostic harm

Inappropriate low-dose steroid or delayed antimicrobial treatment may worsen selected causes, while overtesting non-specific antibodies can mislabel disease.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Repeat corrected acuity, colour and visual fields in each eye with the same methods, documenting the date objective recovery begins.
Monitor the fellow eye and neurological systems for myelitis, brainstem symptoms or additional demyelinating events that change diagnostic classification.
During high-dose steroid treatment, monitor glucose, blood pressure, sleep, mood, infection and gastrointestinal symptoms according to risk and local protocol.
Use OCT and formal perimetry at specialist-defined intervals to quantify structural loss and functional recovery rather than relying on subjective blur alone.
Reconsider the diagnosis promptly if loss progresses beyond the expected window, pain is absent with severe loss or recovery fails to begin.
Provide urgent advice for fellow-eye loss, severe headache, jaw claudication, new weakness, sensory level, sphincter symptoms or persistent vomiting and hiccups.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

The disc may look normal

Most of the optic nerve lies behind the globe. Retrobulbar inflammation can substantially reduce acuity, colour and fields before any visible optic-disc change develops.

Colour can reveal subtle loss

Red desaturation and colour-plate impairment may remain abnormal despite near-normal high-contrast acuity, helping demonstrate asymmetric optic-nerve function.

Uhthoff is not relapse

Temporary worsening of prior demyelinating visual symptoms with heat or exertion can reflect conduction block rather than new inflammation; persistence and new objective signs need specialist review.

MRI protocol is decisive

Routine brain sequences may not suppress orbital fat or cover the full nerve adequately. Explicitly requesting dedicated orbit and optic-nerve imaging protects sensitivity.

Steroids change speed more than destination

In typical demyelinating neuritis, high-dose treatment mainly accelerates recovery. Functional need and atypical antibody-mediated disease make the decision individual rather than automatic.

MS is not inevitable

Future risk depends substantially on brain MRI, prior events and evolving criteria. A clear explanation avoids presenting one optic-neuritis episode as a confirmed lifelong diagnosis.

11Common pitfallsFrequent interpretation and management errors.

01
Calling every painful blurred eye optic neuritis without excluding ocular inflammation and angle closure.
02
Using binocular acuity and missing severe unilateral loss.
03
Assuming a normal optic disc disproves retrobulbar neuritis.
04
Diagnosing multiple sclerosis from optic neuritis without current clinical and MRI criteria.
05
Treating atypical bilateral or severe disease as routine MS-associated neuritis without AQP4 and MOG assessment.
06
Giving low-dose oral corticosteroid or repeated unsupervised courses for unexplained visual loss.
07
Missing giant-cell arteritis because pain occurs with eye movement or inflammatory markers are not striking.