The cornea receives oxygen and nutrients from which combination of sources?

• A. Only from the aqueous humor
• B. From the choroidal circulation
• C. Only from the vitreous humor
• D. The tear film in front of the cornea, the aqueous behind it, and the conjunctival blood vessels

Answer: (D)

The cornea is avascular, so it gets oxygen and nutrients by diffusion from surrounding fluids rather than from blood vessels within the cornea itself. The front surface relies on the tear film to supply oxygen and nutrients to the epithelium. The inner surface relies on the aqueous humor behind the cornea to provide nutrients to the deeper layers and endothelium. The peripheral cornea also receives oxygen and nutrients from the blood vessels of the conjunctiva near the limbus. The choroidal circulation and the vitreous humor do not directly nourish the cornea. So the combination that fits is the tear film in front, the aqueous behind, and the conjunctival vessels.