What are the physical properties of Tear Film?
Physical Properties of Tear Film: The tear film is a three-layered structure as given below:
1) Outermost Layer: Lipid Layer
This layer is secreted by the meibomian glands and is 0.1 mm thick. The main function it performs is to spread over the liquid layer and retard the evaporation of the aqueous layer and maintain the stability of the tear film.
2) Middle Layer: Aqueous Layer
Forms a bulk of the tear film and is secreted by the main and accessory lacrimal glands. It contains essential nutrients and substances necessary for the health and integrity of the cornea. It is approximately 7 mm in thickness.
3) Inner Layer: Mucin Layer
Mucin layer is secreted by the goblet cells of the conjunctiva. This layer is approximately 1 mm thick and functions to convert the hydrophobic corneal epithelium to hydrophilic, allowing the aqueous layer to spread over it.