Your tears are incredibly complex, made up of thousands of molecules in two dynamic layers; the surface oily layer preventing evaporation of your tears and stabilising the tear film; and the inner watery layer lubricating, providing nutrients, and defending against infection.

Normally, tear production and evaporation and drainage are in equilibrium. If something disrupts this balance, it leads to increased tear saltiness, inflammation, potential damage to the ocular surface and symptoms. This vicious cycle is dry eye disease.

If your oily layer is too thin, in between blinks the watery layer is exposed and begins to evaporate. In response you produce more watery tears to protect the integrity of the ocular surface, often leading to wateriness, but not relief of symptoms. This oily layer is produced by meibomian glands in the upper and lower eyelids. Problems with the quality or quantity of oils produced by these glands is called Meibomian Gland Dysfunction (MGD) or posterior blepharitis.

If your watery layer is deficient, there are not enough tears to sufficiently lubricate the eye on blinking, leading to discomfort from friction, and potentially ocular surface damage from dryness