What is the primary source of oxygen that the cornea receives?

The primary source of oxygen for the cornea comes from gaseous exchange with the tear film. The cornea is avascular, meaning it lacks blood vessels, which typically supply oxygen to other tissues in the body. Instead, it relies on oxygen dissolved in the tear film that sits on the surface. The tear film acts as a reservoir, allowing oxygen from the surrounding air to diffuse directly into the cornea.

Additionally, while the aqueous humor provides some nutrients and helps maintain corneal hydration, it is not the main source of oxygen. Similarly, the eyelids play a role in protecting the cornea and helping to maintain moisture but do not directly deliver oxygen to the corneal tissue. Therefore, the gaseous exchange with the tear film is essential for maintaining the health and transparency of the cornea, making it the correct answer.