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
Intraocular penetration of topically-instilled drugs is mainly determined by the corneal: 
Select and explain. 
A. Epithelium, B. Endothelium, C. Stroma, D. Bowman's and Descemet's membrane
A: Epithelium
Answer: A: Epithelium 
Explanation: Ans. Epithelium