Final answer:
The middle layer of tear film is the aqueous layer, whose purpose is to moisten the cornea, provide essential nutrients, remove waste, and protect the eye from infection.
Step-by-step explanation:
The middle layer of the tear film is known as the aqueous layer. Its main purpose is to hydrate the cornea, provide nutrients, and remove waste products. The tear film actually comprises three layers: the lipid layer on the outside, the aqueous layer in the middle, and the mucin layer closest to the eye. The aqueous layer is secreted by the lacrimal glands, and it is the thickest of the three layers, consisting mostly of water along with salts, proteins, and other substances.
This layer is crucial as it helps to maintain a smooth optical surface on the cornea, which is essential for clear vision. It also contains antibacterial substances to protect the eye from infection and foreign objects. The movement of the eyelids when blinking helps to spread the tear film evenly across the surface of the eye, ensuring that the eye remains moist and nourished.
In summary, the middle part of the tear film is known as the aqueous layer and serves to keep the cornea moist, provide nutrition, and help prevent infections through its antibacterial properties.