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 and function of the cornea, which is avascular and relies on the tear film for hydration and the delivery of nutrients and oxygen. The tear film is composed of three layers: the lipid layer, aqueous layer, and mucin layer, each playing a crucial role in maintaining ocular surface health.

The aqueous layer supplies moisture, while the interaction between these layers ensures a smooth optical surface, which is important for clear vision. Moreover, the tear film enhances the movement of the eyelids during blinking, which spreads the moisture across the eye's surface and contributes to the overall comfort and health of the ocular surface.

While the tear film does have indirect roles concerning nutrients and visual acuity by maintaining the cornea's health, the most direct and immediate function focuses on oxygen and moisture provision, making this the best choice among the options provided.