A child with giant papillae under the upper tarsal conjunctiva, limbal Horner-Trantas dots, and a shield ulcer on the superior cornea is diagnosed with vernal keratoconjunctivitis. The mechanism of shield ulcer formation is:

• A Viral cytopathic effect of adenovirus on corneal epithelium
• B Mechanical trauma from giant papillae combined with eosinophil-derived major basic protein cytotoxicity ✓
• C Stromal necrosis from immune complex deposition
• D Limbal stem cell deficiency with epithelial replacement by conjunctival cells

Explanation

VKC shield ulcers form in the superior cornea through a two-hit mechanism: mechanical trauma from giant papillae (cobblestone appearance) abrading the corneal epithelium, combined with toxic damage from eosinophil granule proteins (major basic protein, eosinophil cationic protein) that are directly cytotoxic to epithelial cells. The ulcer has a characteristic oval/shield shape, horizontal orientation in the upper third of cornea, and may accumulate a plaque of mucus and debris. Treatment includes supratarsal steroid injection and occasionally surgical debridement.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.