A 35-year-old man is referred for fundoscopic evaluation of chronic headaches and progressive blurred vision over 3 months. Examination shows bilateral disc swelling with obscured margins, peripapillary retinal folds (Paton's lines), and normal pupillary responses. Visual acuity is preserved. What is the most common cause of this presentation of papilloedema?

## Diagnosis: Idiopathic Intracranial Hypertension (IIH) **Key Point:** Idiopathic intracranial hypertension is the most common cause of papilloedema in young to middle-aged adults, particularly in obese women of childbearing age. ### Clinical Features of Papilloedema (IIH) - **Insidious onset** — progressive over weeks to months - **Bilateral and symmetric** disc swelling - **Preserved visual acuity** — until late stages - **Headache** — diffuse, often worse in morning - **Normal pupillary responses** — RAPD absent - **No pain on eye movements** — distinguishes from papillitis - **Paton's lines** (circumferential retinal folds) — pathognomonic - **Splinter haemorrhages** — circumferential distribution - **Obscured disc margins** with elevated, hyperaemic disc ### Distinguishing Papilloedema from Papillitis | Feature | Papilloedema (IIH) | Papillitis (Optic Neuritis) | |---------|-------------------|---------------------------| | **Onset** | Insidious (weeks–months) | Acute (hours–days) | | **Pain on eye movement** | No | Yes (95%) | | **Visual acuity** | Normal initially | Markedly reduced early | | **RAPD** | Absent | Present | | **Bilaterality** | Bilateral (usually) | Unilateral (typically) | | **Headache** | Present (90%) | Absent or mild | | **Disc appearance** | Swollen, hyperaemic | Hyperaemic, blurred | | **Haemorrhages** | Circumferential, splinter | Peripapillary flame | | **Cause** | Raised ICP | Demyelination, infection | **High-Yield:** IIH is 8–10 times more common in obese women aged 20–40 years. It is the most common cause of papilloedema in this demographic and must be excluded in any patient presenting with papilloedema. ### Diagnostic Criteria for IIH (Modified Dandy Criteria) 1. Signs and symptoms of raised ICP 2. Papilloedema 3. Normal neuroimaging (MRI/CT) excluding venous sinus thrombosis 4. Normal CSF composition 5. Elevated opening pressure on lumbar puncture (>250 mm H~2~O in non-obese, >280 mm H~2~O in obese) **Clinical Pearl:** The preservation of visual acuity despite bilateral papilloedema is a hallmark of IIH. Progressive visual loss suggests impending vision-threatening complications and warrants urgent intervention. **Mnemonic: IIH** — **I**nsidious onset, **I**ncreased ICP (>250 mm H~2~O), **H**eadache with bilateral papilloedema.