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
Keratoconus is associated with all except- 
Select and explain. 
A. Down's syndrome, B. Ehlers-Danlos' syndrome, C. Marfan's syndrome, D. Usher's syndrome
D: Usher's syndrome
Answer: D: Usher's syndrome 
Explanation: Keratoconus may be associated with : Ocular conditions e.g. ectopia lentis, congenital cataract, aniridia, retinitis pigmentosa, and vernal keratoconjunctivitis (VKC).Systemic conditions e.g., Marfan's sysndrome, atopy, Down's syndrome, Ehlers-Danlos syndrome, osteogenesis imperfecta and mitral valve prolapse. Reference:Comprehensive ophthalmology,AK Khurana,4th edition,page no.120