Which layer of the tear film is the thickest?

The aqueous layer is indeed the thickest layer of the tear film. Comprising primarily water, this middle layer serves critical functions, including providing moisture to the eye, delivering nutrients to the cornea, and flushing away debris and pathogens. This layer makes up the majority of the tear film's volume, typically ranging from about 7-10 micrometers in thickness, compared to the thinner lipid and mucin layers.

The lipid layer, while crucial for reducing evaporation of the tear film and maintaining surface tension, is significantly thinner, generally around 0.1 micrometers. Similarly, the mucin layer, which helps with the spreadability and stability of the aqueous layer across the ocular surface, is also thinner than the aqueous layer. This structural hierarchy in thickness highlights the functional importance of the aqueous layer in maintaining overall ocular health. Understanding the distinct roles and proportions of each layer clarifies why the aqueous layer is the dominant component of the tear film.