This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diseases of Cornea, Subject name: Ophthalmology
Most common cause of infectious keratitis in a contact lens user 
Select and explain. 
A. Acanthamoeba, B. Pneumococcus, C. Pseudomonas, D. Staph
C: Pseudomonas
Answer: C: Pseudomonas 
Explanation: Most common cause of infectious keratitis in a contact lens user is pseudomonas Commonest causative organism associated with keratitis - pneumococcus Hypopyon ulcer / ulcus serpens - pneumococcus acanthamoeba : attacks contact lens that are washed with water.