What is the primary function of the precorneal tear film?

The primary function of the precorneal tear film is to provide oxygen and moisture to the eye. This tear film is essential for maintaining the health of the corneal epithelium and plays a crucial role in ensuring that the surface of the eye remains lubricated. It is composed of three layers: an oily outer layer that reduces evaporation, a watery middle layer that provides moisture and nutrients, and a mucous inner layer that helps the tears adhere to the cornea.

By maintaining moisture and delivering essential substances, the tear film aids in protecting the corneal surface, preventing dryness, and ensuring smooth movement of the eyelids over the eye's surface. Furthermore, it plays a role in refracting light, which indirectly supports vision clarity, but its primary role centers on moisture and oxygen supply.

The other options—coloring the eye, protecting against UV rays, and enhancing vision clarity—do not accurately capture the main function of the precorneal tear film. While the tear film contributes to comfort and occasionally aids in visual clarity, its essential function revolves around maintaining moisture and providing oxygen to the eye.