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
Fleischer ring is characteristic of - 
Select and explain. 
A. Megalocornea, B. Diabetes, C. Chalcosis, D. Keratoconus
D: Keratoconus
Answer: D: Keratoconus 
Explanation: In keratoconus slit lamp examination may show thinning and ectasia of central cornea, opacity at the apex and Fleischer's ring at the base of cone, folds in Descemet's and Bowman's membranes. Very fine, veical, deep stromal striae (Vogt lines) which disappear with external pressure on the globe are peculiar feature.Reference:Comprehensive ophthalmology,AK Khurana,4th edition,page no.119