According to the WHO classification of xerophthalmia, corneal ulceration involving one third or more of the corneal surface is staged as:
- A X3B ✓
- B X3A
- C X2
- D XS
Correct answer: A. X3B
Explanation
In the WHO grading, X2 is corneal xerosis, X3C is corneal ulceration involving less than one third of the cornea, and X3B is ulceration or keratomalacia involving at least one third of the cornea. XS denotes corneal scarring and XF denotes xerophthalmic fundus change. The distractor X3C fails because its threshold is strictly less than one third, making extent of ulceration the deciding measurement.
Reference: Khurana, Comprehensive Ophthalmology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.