Which pre-corneal fluid layer is known to increase surface tension and slow evaporation?

The lipid layer is the outermost layer of the tear film and plays a crucial role in maintaining the stability of the tear film as well as slowing the rate of evaporation. Its primary function is to reduce the surface tension of the tear film, which helps prevent tear breakup and maintains a smooth and consistent surface on the cornea.

The lipid layer consists predominantly of lipids (fats) secreted by the meibomian glands located in the eyelids. By forming a thin film over the aqueous layer beneath it, the lipid layer effectively minimizes evaporation of the underlying aqueous component, thereby ensuring that the eye remains lubricated and comfortable. This is particularly important since the aqueous layer, while essential for nourishment and hydration, does not possess the same properties to impede evaporation.

The other layers, such as the mucin layer—which is important for the stability of the tear film and for ensuring the tear film spreads evenly over the corneal surface—do not primarily serve the function of increasing surface tension or reducing evaporation. Ciliary fluid pertains to the fluid produced by the ciliary body but is not involved in creating the tear film layers. Understanding the distinct roles of these layers highlights the importance of the lipid layer in ocular surface health and comfort.