A 28-year-old man who sleeps in his monthly soft contact lenses wakes with severe pain, redness, profuse watery discharge, and blurred vision. Slit-lamp examination shows a central corneal infiltrate with an overlying epithelial defect, surrounding stromal oedema, and a small hypopyon. Gram stain of the corneal scrape shows gram-negative rods. Which organism is most likely?

• A Haemophilus influenzae
• B Staphylococcus epidermidis
• C Streptococcus viridans
• D Pseudomonas aeruginosa ✓

Explanation

Pseudomonas aeruginosa is the classic cause of keratitis in extended-wear and overnight contact lens use. Its proteases and elastase digest stromal lamellae rapidly, producing a fulminant central ulcer with hypopyon within 24 to 48 hours. Staphylococcus epidermidis is the commonest coagulase-negative isolate overall but produces a slower, less virulent infiltrate, so the fulminant overnight-lens presentation points decisively to Pseudomonas.

Reference: Khurana, Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.