Dry Eye is a condition caused by changes in the quantity or quality of your tears. Tears are composed of three main layers that work together to keep your eyes comfortable and protected. If anything affects the balance of these elements, your tears may evaporate too quickly, causing your eyes to feel dry and irritated.
Millions of people suffer from dry eye, making it one of the most common conditions reported to doctors today. Although there is usually no cure for the condition, there are a variety of treatments to soothe its symptoms and to help you feel more comfortable.1
Types of Dry Eye
There are two major types of dry eye:
Aqueous or Mucin Layer Deficiency
This type of dry eye impacts the water portion of the tear film. When you have it, your lacrimal glands don’t produce enough of the watery or mucous component of tears, which makes it harder for your eyes to stay moist and maintain a healthy surface.1,3
Also known as Meibomian Gland Dysfunction (MGD) or blepharitis, this type of dry eye affects the lipid (oil) layer of the tear film–the outermost layer that stabilizes the tear film of your eyes. When you have MGD, your tear film has less oil, so your tears evaporate more quickly. MGD is the most common type of dry eye; more than half of dry eye sufferers have it.1,3,4,8
Tear Film and Dry Eye
Every time you blink, a thin layer of tears is spread across the cornea. This layer of moisture, the tear film, forms a protective coat, lubricating your eyes and washing away any debris that might cause harm or obscure your vision.3
Dry eye occurs when the tear glands stop making enough tears, produce poor quality tears, or the tears evaporate too quickly. As a result, the eye becomes dry and irritation occurs.6,9,10
Three main components are crucial in forming the tear film that coats the cornea:
1. Lipid layer—located on the outermost part of the tear film, the lipid layer stabilizes in the aqueous (watery) layer and prevents it from evaporating too quickly.1-5,7,8
2. Aqueous layer—the largest portion of the tear film, it supplies all the moisture your eyes need to be comfortable.1-4
3. Mucin layer—this innermost layer consists of proteins called mucins that coat the eye and allow the aqueous layer to “stick” to the otherwise water-repellent cornea.1-3,7
All three layers are necessary to create tear film for moist, healthy eyes. If any layer becomes depleted, the tear film cannot properly coat your eyes and dry spots can form, causing your eyes to become symptomatic and uncomfortable.2
1. National Eye Institute. http://www.nei.nih.gov/health/dryeye/factsaboutdryeye.pdf Pages 1, 2. Accessed March 12, 2013.
2. Mayo Clinic. http://www.mayoclinic.com/health/dry-eyes/DS00463/DSECTION=causes Pages 1, 2, 3. Accessed March 5, 2013.
3. 2007 Report of the International Dry Eye WorkShop (DEWS). http://www.tearfilm.org/dewsreport/pdfs/TOS-0502-DEWS-noAds.pdf Page 75, 87.
4. The International Workshop on Meibomian Gland Dysfunction: Report of the Deﬁnition and Classiﬁcation Subcommittee. http://www.iovs.org/content/52/4/1930.full.pdf Pages 1930, 1935.
5. The International Workshop on Meibomian Gland Dysfunction: Report of the Subcommittee on Anatomy, Physiology, and Pathophysiology of the Meibomian Gland. http://www.tearfilm.org/dewsreport/pdfs/TOS-0502-DEWS-noAds.pdf Pages 1338, 1353.
6. Holly F, Lemp MA. Formation and rupture of the tear film. Exp Eye Res 1973; 15: 515-25
7. Bron AJ. Diagnosis of dry eye. Surv Ophthalmol 2001; 45 Suppl 2: S221-6
8. Craig J, Tomlinson A. Importance of the lipid layer in human tear film stability and evaporation. Optom Vis Sci. 1997; 74: 8-13.
9. WebMD. http://www.webmd.com/eye-health/tc/dry-eye-syndrome-topic-overview Accessed March 12, 2013.