In which stage, corneal ulcer involving 1/2 of Corneal surface seen in WHO classification of vitamin A deficiency

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