In 2007, dews recognized dry eye as a disturbance of the Lacrimal Functional Unit (LFU), whose parts act together and not in isolation. It is an integrated system comprising the lacrimal glands, ocular surface (cornea, conjunctiva and Meibomian glands), lids, and the sensory and motor nerves that connect.

Abnormality of any of several subparts of the LFU can be transferred across the entire system through its extensive neural connections to result in an unstable and unrefreshed tear film having altered composition like elevated tear osmolality, presence of pro-inflammatory mediators and proteases, which no longer supports the normal functioning of the ocular surface.

The majority of dry eye symptoms are due to a chronic inflammation of the LFU. This leads to a reduction in the ability of the ocular surface to respond to environmental challenges. The underlying cause of tear film dysfunction is the alteration of tear aqueous, mucin, and lipid components.


1. Lacrimal system is responsible for tear production and drainage

2. Made up of 3 layers

3. Created primarily by lacrimal apparatus and Meibomian glands

4. Lubricate the eyeball, providing oxygen/nutrition for cornea, has antibacterial properties and helps wash away debris

5. Has a unique composition which helps keep surface of cornea slick


Tear fluid nourishes cornea: Glucose, vitamin C, amino acids, minerals, humidity, mucin (viscosity), lipocalin (carries lipids) and lacritin (promotes health of corneal epithelium).

Tear fluid prevents infections: Lysozyme, immunoglobins and lactoferrin.