A 35-year-old woman with a 20-year history of trachoma presents with progressive vision loss. On slit-lamp examination, she has severe corneal scarring with pannus formation and neovascularization. What is the most common site of corneal involvement in trachoma?

## Anatomical Pattern of Trachomatous Corneal Involvement **Key Point:** The superior tarsal conjunctiva is the primary site of chronic inflammation in trachoma, leading to characteristic superior corneal pannus formation and scarring. ### Why Superior Involvement Predominates **High-Yield:** The superior tarsal conjunctiva is preferentially affected because: 1. **Gravity and blinking mechanics:** The upper eyelid moves more extensively during blinking, creating greater mechanical trauma and tear film pooling 2. **Tear film dynamics:** Chlamydial organisms concentrate in the superior fornix 3. **Chronic rubbing:** Patients unconsciously rub the upper lid more frequently, perpetuating infection ### Stages of Trachomatous Corneal Scarring | Stage | Clinical Feature | Mechanism | | --- | --- | --- | | TF (Trachomatous Inflammation-Follicular) | Follicles on upper tarsal conjunctiva | Active infection | | TI (Trachomatous Inflammation-Intense) | Intense inflammation, papillary hypertrophy | Severe active disease | | TS (Trachomatous Scarring) | Linear scars on tarsal conjunctiva | Fibrosis from repeated infection | | TT (Trachomatous Trichiasis) | Inturned lashes from scarring | Entropion from tarsal fibrosis | | TP (Trachomatous Opacity) | Corneal pannus and opacity | Superior corneal involvement | ### Superior Pannus Formation **Clinical Pearl:** The superior corneal pannus is a pathognomonic finding in trachoma, consisting of: - Neovascularization from the superior limbus - Inflammatory cell infiltration (lymphocytes, plasma cells, fibroblasts) - Gradual extension downward if untreated, eventually obscuring the visual axis **Mnemonic:** **SUPerior Pannus in Trachoma = Scarring Upward** — the inflammation starts in the superior tarsal conjunctiva and extends downward onto the superior cornea. ### Progressive Corneal Changes 1. **Early:** Vascularization of superior limbus → pannus formation 2. **Intermediate:** Pannus extends over superior 1/3 of cornea 3. **Advanced:** Pannus may extend to visual axis; Arlt's line (horizontal linear scar at superior tarsal border) becomes visible 4. **Late:** Diffuse corneal scarring, opacity, and blindness **Key Point:** Arlt's line is a horizontal scar at the junction of the upper tarsal and orbital conjunctiva, pathognomonic for previous trachoma and indicates previous severe inflammation.