Which is the innermost layer of the cornea?

• A. Endothelium
• B. Epithelium
• C. Stroma
• D. Descemet's membrane

Answer: (A)

Endothelium is the innermost layer because it lines the back surface of the cornea, facing the anterior chamber. It is a single layer of flat cells that directly interfaces with the aqueous humor. Its main job is to keep the cornea properly dehydrated by actively pumping fluid out of the stroma into the anterior chamber, maintaining transparency essential for vision. If endothelial function is compromised, fluid accumulates in the stroma, causing corneal edema and clouding. Descemet's membrane sits just in front of the endothelium as its basement membrane, so it is not the innermost layer. The other layers—epithelium on the anterior surface and the thick stroma in the middle—are more superficial.