A 4-year-old child presents with a triangular, foamy, silvery-white plaque on the temporal bulbar conjunctiva adjacent to a dry, unwrinkled, lustreless conjunctiva. Night blindness was reported by the mother. This lesion corresponds to which WHO stage of xerophthalmia?

• A X1A, conjunctival xerosis
• B X2, corneal xerosis
• C X1B, Bitot's spot with conjunctival xerosis ✓
• D X3A, corneal ulceration involving less than one third

Explanation

Bitot's spot is a buildup of keratinised epithelium mixed with gas-forming Corynebacterium xerosis bacilli, giving a foamy, triangular, silvery patch on the bulbar conjunctiva, usually temporal. When present together with conjunctival xerosis it defines stage X1C of the WHO xerophthalmia classification. X1A denotes dryness alone without a Bitot's spot, while X2 and X3A involve corneal xerosis and ulceration, which are absent here.

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

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Written and medically reviewed by the StethoPrep medical team.