Final answer:
The outer layer of the tear film is the lipid layer, whose main function is to prevent tear evaporation, maintain eye hydration, and protect against microbial infection.
Step-by-step explanation:
The outer layer of the tear film is known as the lipid layer, which is produced by the Meibomian glands located at the edges of the eyelids. This layer's primary purpose is to prevent the evaporation of the tears, thereby maintaining proper eye hydration and providing a smooth surface for the eye to keep vision clear. Additionally, the tear film serves as a barrier against microbial infection and helps to wash away foreign particles that come into contact with the surface of the eye.