Which clinical feature best distinguishes acute anterior uveitis from acute posterior uveitis?

Explanation

## Distinguishing Anterior from Posterior Uveitis ### Key Clinical Discriminators **Key Point:** Anterior chamber cells and flare are the hallmark findings of anterior uveitis and are absent or minimal in posterior uveitis. This represents the primary anatomical difference in inflammation location. ### Comparative Table | Feature | Anterior Uveitis | Posterior Uveitis | | --- | --- | --- | | **AC cells & flare** | +++++ (prominent) | Absent/minimal | | **Vitritis** | Absent/minimal | +++++ (prominent) | | **Photophobia** | Marked | Absent/mild | | **Pain** | Severe | Minimal/absent | | **Floaters** | Absent | Prominent | | **Blurred vision** | Mild (from AC reaction) | Marked (from vitritis) | | **Anterior synechiae risk** | High | Low | ### Explanation Anterior uveitis causes inflammation in the anterior chamber, producing: - Aqueous flare (protein leak) - AC cells (white cells in aqueous) - Ciliary body irritation → photophobia and pain Posterior uveitis causes inflammation in the vitreous and retina, producing: - Vitritis (vitreous inflammation) - Floaters (from vitreous opacities) - Minimal AC involvement **High-Yield:** On slit-lamp examination, anterior chamber cells graded 0–4+ is the **gold standard discriminator**. Posterior uveitis shows clear aqueous with minimal/no AC cells despite significant vitritis. **Clinical Pearl:** A patient with severe photophobia and pain but clear aqueous (no AC cells) should prompt investigation for posterior uveitis or scleritis, not anterior uveitis. ### Why Other Options Are Misleading - **Vitritis:** Present in posterior uveitis but can occur secondarily in severe anterior uveitis (spillover) - **Photophobia and pain:** Characteristic of anterior uveitis but absent in posterior uveitis — this is a symptom, not a discriminating sign - **Floaters and blurred vision:** Classic posterior uveitis symptoms but can occur in anterior uveitis if vitritis develops