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: 
Select and explain. 
A. Primary and unilateral, B. Primary and bilateral, C. Primary, bilateral, with systemic disease, D. Primary unilateral without systemic disease
B: Primary and bilateral
Answer: B: Primary and bilateral 
Explanation: Corneal dystrophies are primary, bilateral and inherited disorder manifesting occasionally at bih but more usually during first or second decade and sometimes even later in life. Corneal dystrophies are of 3 types: anterior dystrophy, stromal dystrophy and posterior dystrophy.