This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
Diagnostic test for corneal ulcer: March 2005 
Select and explain. 
A. Methylene blue, B. Sodium fluorescein dye, C. Alcian blue, D. Rose Bengal
B: Sodium fluorescein dye
Answer: B: Sodium fluorescein dye 
Explanation: Ans. B: Sodium fluorescein dyeDirect observation under magnified view of slit lamp may reveal the ulcer on the cornea.Fluorescein stain is taken up by exposed corneal stroma and appears green and it helps in defining the margins of the corneal ulcer, and can reveal additional details of the surrounding epithelium.Herpes simplex ulcers show a typical dendritic pattern of staining. Rose-Bengal dye is also used for supra-vital staining purposes, but it may be very irritating to the eyes.