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
A patient using contact lens develops corneal infection. Laboratory diagnosis of acanthamoeba keratitis was established.The following is the best drug for treatment- 
Select and explain. 
A. Propamide, B. Neosporine, C. Ketoconazole, D. Polyhexamethylene biguanide
D: Polyhexamethylene biguanide
Answer: D: Polyhexamethylene biguanide 
Explanation: Polyhexamethylene biguanide PHMB (Drug of choice) Chlorhexidine is an alternative