A 28-year-old woman presents with acute vision loss in the left eye over 48 hours, associated with periocular pain on eye movements. On examination, visual acuity is 6/36 in the affected eye, pupil is relatively afferent, and fundoscopy reveals hyperaemia and blurring of the optic disc margins with peripapillary flame haemorrhages. Intraocular pressure is normal. What is the most appropriate next step in management?

Explanation

## Clinical Diagnosis: Optic Neuritis (Papillitis) The clinical presentation is classic for **optic neuritis** (inflammation of the optic nerve head): - Acute unilateral vision loss with pain on eye movement (retrobulbar component) - Relative afferent pupillary defect (RAPD) indicating optic nerve dysfunction - Disc hyperaemia with peripapillary haemorrhages (papillitis = optic neuritis with visible disc involvement) - Normal intraocular pressure excludes acute glaucoma ### Differential: Papilloedema vs Papillitis | Feature | Papilloedema | Papillitis | |---------|--------------|----------| | **Onset** | Insidious (weeks–months) | Acute (hours–days) | | **Vision** | Often normal initially | Acute loss, central scotoma | | **Pain** | Absent | Present (periocular, on eye movement) | | **RAPD** | Absent (bilateral) | Present (unilateral) | | **Cause** | Raised ICP | Demyelination, infection, inflammation | | **Prognosis** | Depends on ICP cause | Often good with treatment | ## Management Algorithm for Suspected Optic Neuritis ```mermaid flowchart TD A["Acute unilateral vision loss<br/>+ disc hyperaemia + pain"]:::outcome --> B{"MRI brain & orbits<br/>already done?"}:::decision B -->|No| C["Urgent MRI brain & orbits<br/>to exclude MS, tumour, infection"]:::action C --> D{"Lesion found?"}:::decision D -->|Yes| E["Treat underlying cause<br/>+ IV methylprednisolone"]:::action D -->|No| F["Consider LP if MS risk<br/>or atypical features"]:::action B -->|Yes, normal| G["Oral corticosteroids<br/>+ VEP + MRI spine"]:::action E --> H["Neurology referral"]:::action F --> H G --> H ``` ## Next Step Rationale **Key Point:** The ONTT (Optic Neuritis Treatment Trial) and current neuro-ophthalmology guidelines recommend: 1. **MRI brain and orbits** (first-line imaging) - Excludes demyelinating lesions, intracranial mass, infection - Identifies white matter lesions (MS risk stratification) - Assesses optic nerve enhancement 2. **Lumbar puncture** (conditional) - Performed if MRI is normal AND MS is suspected - Identifies oligoclonal bands, elevated IgG index - Not routine in all cases; reserved for diagnostic uncertainty 3. **Visual Evoked Potentials (VEP)** - Confirms demyelinating conduction block - Prognostic value; delayed latency 4. **Corticosteroids** - Initiated after imaging (to avoid masking serious pathology) - Oral prednisolone 1 mg/kg/day × 2 weeks, then taper - IV methylprednisolone if severe vision loss or atypical presentation **High-Yield:** Option 3 (oral steroids + VEP) skips neuroimaging — **dangerous** because it does not exclude intracranial lesions (MS, tumour, infection). Option 1 (MRI alone) is incomplete; LP may be needed if imaging is normal. Option 2 (LP first) is not standard — imaging must precede LP to exclude mass effect. **Clinical Pearl:** Periocular pain with eye movement is the hallmark of retrobulbar optic neuritis and strongly suggests demyelination, not papilloedema (which is painless). **Warning:** Do NOT give corticosteroids before imaging — you may mask or delay diagnosis of a treatable mass or infection. [cite:Harrison 21e Ch 428]