system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
In which stage, corneal ulcer involving 1/2 of Corneal surface seen in WHO classification of vitamin A deficiency
assistant
The correct answer is  WHO classification of Vitamin A deficiency:
I Primary changes
X1A ⇒ Conjunctival xerosis
X1B ⇒ Bitot's spots
X2 ⇒ Corneal xerosis
X3A ⇒ Corneal ulcer < 1/3 rd of corneal surface
X3B ⇒ Corneal ulcer > 1/3rd of corneal surface.
II Secondary changes
XN ⇒ Night blindness
XF ⇒ Xeropthalmic fundus
XS ⇒ Xerophthalmia - related corneal Scar