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
Thining of cornea occurs in - 
Select and explain. 
A. Megalocornea, B. Bullous keratopathy, C. Endothelial dystrophy, D. Keratoconus
D: Keratoconus
Answer: D: Keratoconus 
Explanation: Keratoconus (conical cornea) is a noninflammatory bilateral (85%) ectatic condition of cornea in its axial pa. It usually stas at pubey and progresses slowly. Etiopathogenesis. It is still not clear. Various theories proposed so far label it as developmental condition, degenerative condition, hereditary dystrophy and endocrine anomaly. Essential pathological changes are thinning and ectasia which occur as a result of defective synthesis of mucopolysaccharide and collagen tissue. Reference:Comprehensive ophthalmology,AK Khurana,4th edition,page no.119