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
Keratoconus is associated with all except – 
Select and explain. 
A. Down's syndrome, B. Ehlers–Danlo's syndrome, C. Marfan's syndrome, D. Usher's syndrome
D: Usher's syndrome
Answer: D: Usher's syndrome 
Explanation: Systemic conditions associated with keratoconus are a marfan syndrome, osteogenesis- imperfecta, EDS, Down's syndrome, MVP, atophy (asthma, eczema, atopic keratoconjunctivitis, hay fever).