What is the main source of oxygen for the corneal epithelium?

The primary source of oxygen for the corneal epithelium is the tear film. The cornea is avascular, meaning it does not have its own blood supply; therefore, it relies on other sources to obtain essential nutrients and oxygen. The tear film provides a direct supply of oxygen dissolved in the tears, which is crucial for the metabolic processes of the epithelial cells.

Additionally, oxygen from the atmosphere can also reach the cornea, particularly when the eyes are open. However, when the eyes are closed, or during contact lens wear, the tear film becomes even more critical, as it maintains a consistent supply of oxygen to the corneal cells.

While blood vessels could be a source of oxygen in other tissues, they do not supply the cornea directly since it lacks blood vessels. Contact lenses can limit the amount of oxygen that reaches the cornea, making the role of the tear film even more significant in those scenarios. Thus, the tear film stands out as the main and most reliable source of oxygen for the corneal epithelium.