Optic Neuritis and Optic Neuropathies
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Direct answer
Optic neuritis is acute inflammatory demyelination of the optic nerve, typically causing painful unilateral vision loss with a relative afferent pupillary defect in young adults. It carries a substantial long-term risk of multiple sclerosis, and intravenous steroids speed recovery without changing final visual outcome. Other optic neuropathies, including ethambutol toxicity, ischaemic optic neuropathy and giant cell arteritis, are separated by age, pattern and systemic features.
What you must remember
- Pain on eye movement: characteristic of retrobulbar optic neuritis and present in most patients, typically worse on movement.
- Relative afferent pupillary defect: a unilateral afferent defect that persists even when the fundus looks normal, so it is elicited with the swinging flashlight test.
- Colour vision: red desaturation is typical and may be out of proportion to the loss of acuity.
- Central scotoma: the typical field defect is central or paracentral, rather than a generalised loss.
- MS risk: in the classic Optic Neuritis Treatment Trial, about half of patients developed multiple sclerosis within 15 years, and MRI lesions raise the risk.
- Ethambutol toxicity: dose-dependent optic neuropathy with bilateral centrocaecal scotomas and red-green loss, usually reversible if the drug is stopped early.
- NAION: sudden painless monocular vision loss with an altitudinal field defect and disc swelling in older patients with vascular risk.
- Giant cell arteritis: an emergency in older patients with sudden vision loss, needing immediate high-dose steroids before biopsy, with raised ESR and CRP.
A comparison of three optic nerve disorders
Optic nerve disorders differ in age, pain, disc appearance and recovery, and these features narrow the diagnosis at the bedside. The table compares the three conditions most often examined together. Every such patient needs the pupils, disc and visual fields documented, because the same complaint of sudden blurring can have very different causes.
| Feature | Optic neuritis | NAION | Giant cell arteritis |
|---|---|---|---|
| Typical age | Young adults, often women | Older, with vascular risk | Over 50 years |
| Pain | Pain on eye movement | Painless | Headache, jaw claudication |
| Disc | Normal, or swollen if papillitis | Swollen, often sectoral | Swollen, later pale |
| Visual field | Central or paracentral scotoma | Altitudinal defect | Variable |
| Recovery | Usually good over weeks | Poor | Poor if steroids are delayed |
| Urgent action | MRI and MS counselling | Control vascular risk | ESR, CRP and steroids now |
Optic neuritis is the young, painful and usually recovering picture, while NAION is abrupt, painless and older. Giant cell arteritis is the emergency, because delayed steroids can cost the second eye. Any older patient with new headache, scalp tenderness and visual loss needs ESR and CRP checked the same day.
Where the exam tries to catch you
Most traps in this area depend on a single sign that is easy to miss or to over-read.
- Trap: Assuming a normal fundus excludes optic neuritis Correct: retrobulbar neuritis has a normal disc, so the diagnosis rests on the pupil, colour vision, field loss and MRI.
- Trap: Using high-dose steroids to improve final vision Correct: steroids speed recovery, but final visual acuity is similar to untreated patients in the classic trial.
- Trap: Continuing ethambutol after new colour vision loss Correct: stop the drug promptly, since the optic neuropathy is usually reversible when caught early.
- Trap: Missing giant cell arteritis in an older patient with sudden vision loss Correct: start high-dose steroids immediately after bloods are drawn, without waiting for temporal artery biopsy.
Frequently asked questions
Which clinical sign localises a lesion to the optic nerve?
A relative afferent pupillary defect localises a lesion to the optic nerve or retina on the affected side. It is present even when the fundus looks normal in retrobulbar optic neuritis. It is best elicited with the swinging flashlight test.
Which drug causes dose-dependent optic neuropathy in tuberculosis treatment?
Ethambutol causes dose-dependent optic neuropathy, with reduced visual acuity, red-green colour loss and bilateral centrocaecal scotomas. The risk rises at higher daily doses, and early discontinuation usually leads to recovery. Visual acuity and colour vision are checked before and during treatment.
How does NAION differ from giant cell arteritis?
NAION is an ischaemic optic neuropathy in older patients with vascular risk factors, typically painless and without systemic symptoms. Giant cell arteritis is a systemic vasculitis with headache, jaw claudication and raised ESR and CRP, and it is a medical emergency. Suspected giant cell arteritis needs immediate steroids to protect the second eye.
Does corticosteroid treatment change the final visual outcome in optic neuritis?
Intravenous methylprednisolone in optic neuritis speeds visual recovery but did not change final visual acuity at long-term follow-up in the classic trial. Its main role is faster recovery in selected patients. Steroid decisions are made with the clinical team because of side effects and recurrence risk.
What is the risk of multiple sclerosis after optic neuritis?
Around half of patients with optic neuritis in the classic Optic Neuritis Treatment Trial developed multiple sclerosis within 15 years. MRI lesions at presentation raise the risk substantially. This is why optic neuritis is a key prompt for MRI of the brain.