Why do the corneal opacities in adenoviral keratitis look coin-shaped?
-After the acute infection, viral antigens remain in the anterior stroma
-The immune system mounts a delayed response, producing round subepithelial infiltrates of lymphocytes and macrophages beneath the healed epithelium — giving the classic coin- shaped appearance
-The corneal epithelial lesions from adenovirus are initially focal, round epithelial cell clusters where viral antigen gets deposited
-When these heal, the antigen remains in a circular
distribution in the anterior stroma directly beneath each epithelial focus
-The immune system (lymphocytes + macrophages) organizes an infiltrate around that antigen focus, which naturally forms a well-circumscribed round lesion because of the way corneal keratocytes and collagen lamellae constrain the spread
-Other shapes (linear, geographic) occur when lesions are epithelial ulcers (e.g., HSV dendrites), but in adenovirus, because the trigger is 'antigen islands' under epithelium, the infiltrates look like tiny round coins
Image from Rajan Eye Care Hospital
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