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
Keratitis is caused by ? 
Select and explain. 
A. Bacteria, B. Atopy, C. Protozoa, D. All
D: All
Answer: D: All 
Explanation: Ans. is 'd' i.e., All Causes of keratitis 1. Infective keratitis Bacterial Viral Fungal Chlamydial Protozoal Spirochaetal 2. Allergic keratitis Phlyctenular keratitis Vernal keratitis Atopic keratitis 3. Trophic keratitis Exposure keratitis Neuroparalytic keratitis Keratomalacia Atheromatous ulcer 4. Keratitis associated with diseases of skin and mucous membrane. 5. Keratitis associated with systemic collagen vascular disorders. 6. Traumatic keratitis, which may be due to mechanical trauma, chemical trauma, thermal burns, radiations. 7. Idiopathic keratitis e.g., Mooren's corneal ulcer Superior limbic keratoconjunctivitis Superficial punctate keratitis of Thygeson