## Histopathology of Active Trachoma **Key Point:** The hallmark of active trachoma (TF stage) is the presence of follicles composed of lymphocytes and plasma cells, often with a central area of necrosis or fibrin deposition. ### Histological Stages of Trachoma | Stage | Histology | Clinical Appearance | |-------|-----------|---------------------| | TF (Active) | Lymphoid follicles with central necrosis, lymphocytes, plasma cells | Red, inflamed upper tarsal conjunctiva with follicles | | TI (Intense) | Dense lymphoid infiltration, epithelial damage | Severe papillary inflammation, intense redness | | TS (Scarring) | Subepithelial fibrosis, loss of goblet cells, keratinization | Horizontal linear scars (Arlt's line) | | TT (Trichiasis) | Fibrosis with misdirected lashes | Inturned eyelashes | | TE (Entropion) | Severe fibrosis, eyelid structural collapse | Eyelid inversion | **High-Yield:** The **follicle** is the diagnostic hallmark of active trachoma. Follicles are lymphoid aggregates that appear as pale, slightly raised lesions on the upper tarsal conjunctiva. They are NOT specific to trachoma (also seen in viral conjunctivitis, inclusion conjunctivitis) but in the context of endemic areas and chronic course, they are pathognomonic. **Clinical Pearl:** Arlt's line (a horizontal scar on the upper tarsal conjunctiva) appears in the scarring stage (TS), not in active TF. This is a late finding indicating previous chronic infection and fibrosis. **Mnemonic:** **TFITS** for trachoma stages — **T**rachomatous inflammation–**F**ollicular, **I**ntense, **T**richiasis, **S**carring (and **E**ntropion). 
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