This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cornea, Subject name: Ophthalmology
[{'content': 'Indications to use Collagen cross linking \nSelect and explain. \nA. Herpes infection, B. Fungal corneal ulcer, C. Pachymetry less than 400 nm, D. Severe dry eye', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Riboflavin is used in collagen cross linking for keratoconus COLLAGEN CROSS LINKING C3R: Principle: Using riboflavin, we build up collagen cross links and provide cornea the strength to maintain its curvature f/b use contact lenses for few days. UV-A radiation 370 nm is used for 45 minutes. Indication: Keratoconus Post lasik ectasia Fungal corneal ulcer Corneal ectatic disorders CONTRAINDICTION Herpes infection Pachymetry less than 400 nm Severe dry eye', 'role': 'assistant'}]