Key Points

• Optic Neuritis (ON) is inflammation of the optic nerve, most commonly caused by demyelinating disorders 
• It is a common presenting feature of Multiple Sclerosis but other, rarer, causes exist
• Typical presentation is acute retrobulbar pain, worse on eye movement, followed by central, unilateral vision loss that worsens over hours/days and starts to resolve within 2 weeks 
• On examination look for RAPD, impaired colour vision and a central visual field defect
• Steroid treatment is not routinely indicated for typical ON.

Introduction

Optic neuritis is an inflammatory disorder of the optic nerve (CN II), disrupting its ability to transfer information from the retina to the brain. It leads to acute, central vision loss with ocular pain made worse on eye movement. 

Risk factors² for typical optic neuritis include:

• Female sex (3:1 ratio)
• Younger people (20-50)
• Multiple Sclerosis (MS) (presenting feature in 20% of cases)

Around 50% of all patients with MS will experience an episode of optic neuritis at some point¹.

Other, more atypical, causes include systemic autoimmune conditions, infections or toxic neuropathy. 

Pathophysiology

Typical optic neuritis is an autoimmune and inflammatory process¹.

1. T-Cell Activation: Immune cells are incorrectly primed to see myelin antigens as foreign. They cross the blood- brain barrier and attack the myelin sheath. 
2. Demyelination: This attack causes acute inflammation and strips the nerve of its myelin sheath.
3. Signal Disruption: Myelin is essential for rapid, efficient nerve signal conduction. Without it, the electrical signals from the retina are slowed, distorted, or blocked entirely.

This mechanism is similar to the demyelination process that occurs in the brain and spinal cord in MS, which is why typical optic neuritis is so strongly associated with it.

Signs and Symptoms 

Symptoms: ^3,4

• Acute central vision loss in one eye. Often described as a “smudge” in central vision. 
• Pain in the eye made worse on eye movement 
• Decreased colour perception. Patients will report colours looking “washed out” 
• Visual recovery: following the acute phase (3-7 days), vision will slowly start to recover spontaneously with or without treatment. Some patients will be left with residual defects. 

Atypical red flag: Bilateral vision loss in typical optic neuritis can happen, but care must be taken to rule out more atypical underlying conditions such as neuromyelitis optica spectrum disorders (NMOSD).

Fig. 1 – decreased colour perception and central vision loss ⁶

Examination signs: ^1,5

• Visual acuity: can range from mild impairment (more in typical ON) to complete vision loss (more indicative of atypical ON).
• Relative Afferent Pupillary Defect (RAPD): a diminished pupillary response of the affected eye to bright light. 
• Impaired colour vision: tested with Ishihara plates, most commonly affecting ability to differentiate the colour red. 
• Fundoscopy: normal in 2/3 of typical ON cases (retrobulbar neuritis, not affecting optic disc), with 1/3 of typical ON cases showing papillitis (swollen disc with blurred margins) 
• Visual field defect: central vision loss is most common. 

Optic neuritis is a clinical diagnosis in patients with typical signs. An MRI of the brain and orbit with FLAIR sequencing can confirm the diagnosis and help look for white matter lesions suggestive of MS.

In atypical cases, additional laboratory testing may be required to establish the aetiology².

Management

Treatment with IV methylprednisolone for 3 days, followed by an oral prednisolone tapering regime ^2,3 should be started if: 

• you suspect non- infective atypical ON
• Typical ON with:
  • visual acuity is < 6/12 at 1 week and the patient only has one functional eye
  • the patient has an occupational need for good vision e.g. driving

However, steroid treatment is not routinely indicated for typical ON.

Refer the patient to ophthalmology and neurology, who can guide further treatment. This is especially important when considering atypical causes or preventing relapse by initiating disease- modifying therapy for MS.  

Optic Neuritis Treatment Trial 

This treatment regimen was studied in the Optic Neuritis Treatment Trial (ONTT) and was found to speed up visual loss recovery and have slightly better visual outcomes at 6 months when compared to just oral steroid treatment.⁶ Importantly, it found that giving oral prednisolone without preceding IV methylprednisolone almost doubled the risk of recurrence. If starting steroid treatment, always give IV first. 

Prognosis

The prognosis for typical ON is good, with most patients experiencing significant visual recovery within 6 months. 

References:

1. Guier CP, Stokkermans TJ. Optic Neuritis [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2025. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557853/
2. Optic neuritis – Symptoms, diagnosis and treatment | BMJ Best Practice [Internet]. bestpractice.bmj.com. Available from: https://bestpractice.bmj.com/topics/en-gb/966
3. Bowling B, Kanski JJ. Kanski’s clinical ophthalmology: a systematic approach. 9th ed. Edinburgh: Elsevier; 2019.
4. Alastair K O Denniston, Murray PI. Oxford handbook of ophthalmology. 4th ed. Oxford, United Kingdom; Oxford University Press; 2018.
5.  Beck RW, Cleary PA, Anderson MM, Keltner JL, Shults WT, Kaufman DI, et al. A Randomized, Controlled Trial of Corticosteroids in the Treatment of Acute Optic Neuritis. New England Journal of Medicine. 1992 Feb 27;326(9):581–8.
6. Image generated using Google Gemini Nano Banana, prompt: “An image of two telephone boxes, one with decreased colour saturation and a blurry central spot”

Written by Dr Jan Arszulowicz (FY1) and reviewed by Dr Dr Alice Bellchambers (ST5, Ophthalmology)