This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cornea and sclera, Subject name: Ophthalmology
[{'content': 'Immune ring is a feature of - \nSelect and explain. \nA. Interstitial keratitis, B. Fungal corneal ulcer, C. Bacterial corneal ulcer, D. Herpes simplex keratitis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: A sterile immune ring (yellow line of demarcation)may be present where fungal antigen and host antibodies meet.Its a sign in fungal corneal ulcer Reference:Comprehensive ophthalmology,AK Khurana,6th edition,page no.106', 'role': 'assistant'}]