The Anatomy of Evaporative Dry Eye
Tears are made up of three layers:
- Lipid (oil) layer: lubricates and prevents evaporation
- Aqueous (water) layer: nourishes and protects the cornea
- Mucin layer: adheres tears to the eye
Meibomian glands in the eyelid create the lipid (oil) layer of the tear film. Evaporative Dry Eye disease is most often caused by a blockage or obstruction in the eyelid glands, which can lead to a lipid deficiency in the tears.
The meibomian glands
As the tear film is exposed directly to air, tears rely upon a protective, oily layer to reduce evaporation, maintain volume and aid lubrication. If this protective layer of the tear film is compromised, the corneal surface can also become compromised.2
Until recently, little attention has been paid to the role of the oil or protective lipid layer of the tear film. Now, recognition is being given to a common condition in dry eye patients: blockage of the lipid-producing meibomian glands.
Meibomian Gland Dysfunction
Meibomian Gland Dysfunction results from the formation of keratotic plugs, which obstruct gland orifices and limit the secretion of individual glands. It may be accompanied by signs of eyelid inflammation (such as swelling or redness) – or it may occur in the absence of obvious external signs, and might not be immediately evident, even when examined by a doctor with the magnification of a microscope.3-4
Risk factors
Hormonal changes in women during menopause, particularly changing levels of estrogen, can cause thickening of the oils secreted by the meibomian glands, which results in obstructed glands. Also, decreased estrogen levels may enhance conditions under which staphylococcal bacteria can proliferate, causing migration of the bacteria into the glands. This results in a decreased secretion rate. Additional factors that may cause or exacerbate meibomian gland disease include age, contact lens wear and hygiene, cosmetic use, and other illnesses, particularly diabetes.3-9
