(a) When removing the ulcer, the knife should be kept in parallel with the cornea surface to cut the white fiber between the lesion and the residual cornea. (b) The margin is a slope and the surface is smooth after keratectomy. The injection is from the clear cornea of the lesion edge. The needle is inserted toward the lesion center in parallel with the stroma. The bevel of the needle is in the corneal stroma completely.