A 55-year-old woman with previous herpes zoster ophthalmicus has a well-demarcated oval epithelial defect with rolled grey edges in the interpalpebral zone. The surrounding stroma is smooth and clear, she reports almost no pain, and measurement of corneal touch threshold shows grossly elevated sensation thresholds. The fundamental mechanism of this ulcer is:

• A Immune complex mediated destruction of stromal collagen
• B Loss of sensory trophic innervation leading to impaired epithelial healing ✓
• C Direct cytopathic replication of virus within corneal epithelial cells
• D Tear film instability secondary to cicatricial lid shortening

Explanation

This is a neurotrophic (neuroparalytic) keratopathy. Damage to the ophthalmic division of the trigeminal nerve deprives the epithelium of sensory axons that mediate trophic support, producing a painless, indolent epithelial defect with rolled edges and absent spontaneous healing. Direct viral cytopathic effect characterises the earlier dendritic stage, which is painful, making option C the key distractor.

Reference: Kanski's Clinical Ophthalmology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.