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
Corneal dystrophies are usually – 
Select and explain. 
A. Primarily unilateral, B. Primarily bilateral, C. Primarily unilateral without systemic disease, D. Primarily bilateral with systemic disease
B: Primarily bilateral
Answer: B: Primarily bilateral 
Explanation: "A corneal dystrophy is classically bilateral, progressive, and isolated to the cornea. The disorder is inherited, characteristically in a dominant fashion, and often appears clinically to involve only one layer of the cornea "...Yanoff