This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Retina, Subject name: Ophthalmology
Calcification is seen in all of the following except: 
Select and explain. 
A. Persistent hyperplastic primary vitreous, B. Retinoblastoma, C. Choroidal osteoma, D. Optic nerve head drusen
A: Persistent hyperplastic primary vitreous
Answer: A: Persistent hyperplastic primary vitreous 
Explanation: All of the following have characteristic calcification as a sign of identification except persistent hyperplastic primary vitreous. Ocular Structures that can have Calcification Concretions In conjunctiva Optic nerve head drusen Retinoblastoma Choroidal Osteoma Pthisical eyeball Band shaped keratopathy