A 60-year-old man presents with a central oval corneal ulcer with sharply demarcated edges, dense yellowish-white infiltration, and a 2 mm level of pus in the anterior chamber. There is no history of trauma or contact lens use. The most likely causative organism is:

• A Pseudomonas aeruginosa
• B Aspergillus fumigatus
• C Streptococcus pneumoniae ✓
• D Haemophilus influenzae

Explanation

The classical hypopyon corneal ulcer of the elderly is caused by Streptococcus pneumoniae (pneumococcus). It produces a central oval ulcer with sharply defined margins and a sterile hypopyon formed by fibrin and leucocytes attracted by pneumococcal toxin. The hypopyon does not indicate intraocular infection. Fungal ulcers have feathery margins with satellite lesions, and Pseudomonas is linked to contact lens wear with rapid liquefactive necrosis.

Reference: Parsons' Diseases of the Eye, 23rd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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