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
The commonest cause of keratitis in soft contact lens users is – 
Select and explain. 
A. Acanthamoeba, B. Staph aureus, C. Naegleria, D. Herpes
A: Acanthamoeba
Answer: A: Acanthamoeba 
Explanation: "Pseudomonas aeruginosa is the most common organism encountered in contact lens-related acute keratitis and corneal ulcer".
- Holland & mannis
Acanthamoeba is the 2nd most common cause.