A 48-year-old man with chronic blepharitis presents with bilateral ocular irritation. Examination shows multiple white infiltrates near the limbus, each separated from the limbus by a clear zone, with intact overlying epithelium. What is the underlying mechanism?
- A Hypersensitivity reaction to staphylococcal exotoxin ✓
- B Direct invasion by coagulase-positive staphylococci
- C Peripheral corneal ischaemia from vasculitis
- D Mechanical abrasion by misdirected lashes
Correct answer: A. Hypersensitivity reaction to staphylococcal exotoxin
Explanation
Staphylococcal marginal keratitis is a Type III and IV hypersensitivity response to exotoxins and cell wall antigens of S. aureus, producing infiltrates at the limbus separated by a clear interval, with intact epithelium. Direct bacterial invasion would produce an epithelial defect and positive cultures, which is not typical here.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.