A 35-year-old woman with longstanding trachoma presents with progressive vision loss and photophobia. On slit-lamp examination, she has trichiasis and corneal scarring. Which is the most common site of corneal involvement in trachoma?

Explanation

## Corneal Involvement in Trachoma: Site Predilection **Key Point:** The **superior cornea** is the most common site of corneal involvement in trachoma, characterised by pannus formation (vascular infiltration) and subsequent scarring. ## Pathophysiology of Corneal Damage **High-Yield:** Trachomatous pannus develops at the superior limbus and extends downward over the cornea. This occurs because: 1. Chronic inflammation of the upper tarsal conjunctiva (site of maximum chlamydial load) 2. Vascular and inflammatory cell infiltration from the superior limbus 3. Progressive fibrosis and scarring of the superior cornea 4. Entropion and trichiasis from upper lid scarring cause mechanical abrasion ## Stages of Corneal Involvement | Stage | Location | Pathology | Vision Impact | |-------|----------|-----------|---------------| | **Early** | Superior limbus | Pannus (hyperemia, neovascularization) | Minimal | | **Progressive** | Superior cornea extending centrally | Scarring, opacity | Moderate | | **Advanced** | Central cornea | Dense opacity, leukoma | Severe/blindness | | **Chronic** | Entire cornea | Trichiasis, entropion, mechanical trauma | Irreversible blindness | **Clinical Pearl:** The **superior cornea is preferentially involved** because: - Upper tarsal conjunctiva has higher bacterial load and chronic inflammation - Pannus extends from superior limbus downward - Upper lid entropion and trichiasis cause mechanical abrasion of superior cornea - This creates a characteristic "superior corneal scarring" pattern pathognomonic for trachoma ## Why Other Sites Are Less Common **Mnemonic:** **SUPERIOR = Scarring in Trachoma** - **Inferior cornea**: Rarely involved primarily; may be affected secondarily by inferior trichiasis but less common than superior involvement - **Central cornea**: Opacity develops late as pannus extends centrally; not the primary site - **Limbal region**: While pannus originates at the limbus, the **corneal extension** is superior, not the limbus itself being the "site of involvement" **Warning:** Do not confuse "limbal pannus" (the origin of vascular infiltration) with "corneal involvement" (the actual scarring and opacity). The question asks for the most common **corneal site**, which is the **superior cornea**.