## Distinguishing Papilloedema from Papillitis ### Key Differences in Visual Function **Key Point:** Papilloedema characteristically preserves visual acuity in early to moderate stages, whereas papillitis causes early and significant visual loss. ### Comparison Table | Feature | Papilloedema | Papillitis | | --- | --- | --- | | **Visual Acuity** | Normal (early–moderate) | Reduced early | | **Afferent Pupillary Defect (APD)** | Absent | Present | | **Disc Margin Blurring** | Yes (circumferential) | Yes (may be focal) | | **Disc Hyperaemia** | Yes | Yes | | **Colour Vision** | Normal | Impaired (red desaturation) | | **Central Scotoma** | Absent | Common | | **Cause** | Raised intracranial pressure | Inflammation of optic nerve head | ### Clinical Pearl **Clinical Pearl:** The **preservation of visual acuity despite disc swelling** is the hallmark of papilloedema and reflects the *passive* nature of the swelling (increased ICP transmitted to the nerve). In contrast, papillitis involves *active inflammation* of the nerve tissue itself, leading to early functional loss. ### High-Yield Mnemonic **Mnemonic: PAPILLOEDEMA = Pressure (ICP) → Acuity Preserved** **Mnemonic: PAPILLITIS = Inflammation → Acuity Poor** ### Why Other Options Are Incorrect - **Blurring of disc margins:** Both papilloedema and papillitis cause disc margin blurring due to swelling. - **Optic disc hyperaemia:** Both conditions show hyperaemia from increased vascularity and inflammation. - **Afferent pupillary defect:** This is seen in papillitis (nerve dysfunction) but NOT in papilloedema (passive ICP effect). ### Pathophysiology Summary Papilloedema results from raised intracranial pressure compressing axonal transport at the optic disc, causing swelling without nerve fibre death in early stages. Papillitis is inflammation of the optic nerve head (often demyelinating), causing both swelling and axonal damage, hence early vision loss and APD. 
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