Dry, itchy eyes, or "Dry Eye Syndrome" is the most common complaint that eye doctors hear from patients. Americans of both sexes, of all ages, and of all racial backgrounds have mild or severe instances of dry itchy eyes.
The eyes often reflect a larger problem that needs to be treated systemically. Certain nutrients such as vitamins A, C, D, E, & B6, Magnesium, GLA & DHA, Mucopolysaccharides (mucopolysaccharides are sugar molecules clumped together in a long chain) & tumeric may help ease chronic and severe dry eyes.
Dry itchy eyes are often related to other health conditions in the body such as other mucous membrane dryness, brittle nails, and in interior surfaces like the joints. The condition can an indicator of digestive imbalances or of serious autoimmune diseases, like Sjogren's syndrome, rheumatoid arthritis, or lupus erythematosus.
Next: Nutritional support, diet, & lifestyle tips for dry eyes.
Symptoms typically include irritation, dryness, burning, grittiness, difficulty reading for long periods of time, and, even though it may seem contradictory, excessive watering or tearing as the eyes attempt to solve the problem.
There are three interrelated layers of the "tear film" - the moisture laden surface of the eye and continuity of that surface and the production of tears relies on the function of three interrelated layers:
- Mucus layer which has some anti-microbial properties.
- Slightly alkaline watery layer comprising up 90% of the thickness of the tear film.
- Oily layer which slows evaporation of the tear film.
- Blinking renews the tear film by bringing material from the watery and oily layers removing debris. While normal blink rate is about 10-12 blinks per minute, when working on the computer our blink rate often slows. After about 10 seconds the tear film becomes unstable - leading to tired, dry eyes. This is also partially true when the blink is incomplete - not fully covering the cornea. It is the cornea that tells the brain to send messages to the body to produce more or less tears and when to blink.
Causes of Dry Eyes
- Any disruption in the tear production process. known as aqueous tear-deficient dry eye wherein the lacrimal glands don't produce enough tear fluid.
- LASIK surgery temporarily disrupts the normal activity of the tear film mechanism. Also, during LASIK, about 60-70% of the superficial nerve fibers in the cornea are cut, which affects both sensing of dryness and production of aqueous tears. As a result the rate of blinking can slow so much that the tear film deteriorates before the next blink reconstitutes it. The end result may be many months of mild to severe symptoms. Eventually, this situation usually heals itself.
- Tear evaporation known as evaporative dry eye, which may result from meibomian gland inflammation.
- Blepharitis with inflammed eyelids can cause dry itchy eye symptoms.
- Computer Users tend to blink much less frequently (about 3-4 times per minute verses the normal about 10-15 times per minute). This causes increased tear film instability and evaporation accompanied by eye strain and fatigue that comes of staring at a computer screen. The position of the monitor below eye level allow the upper eyelid to cover more of the eye's surface protecting the tear film from evaporation.
- Researchers have found that patients with this form of dry eye syndrome have lower corneal cell nerve dendrite density and various other features of corneal structures such as nerve fiber length, thickness, etc.3
- Other diseases that may be connected to dry eyes are Diabetes, (especially with high blood sugar), migraine headaches,1 Rheumatoid Arthritis, Thyroid disease (lower lid does not move when blinking), Asthma, Lupus, and possibly Glaucoma and
- Age: Dry itchy eyes are experienced by 75% of those over 65, by which time you have 40% of the volume of tear film that you had when you were 18.
- Women's hormonal changes can cause lowered tear production. During the first part of the menstrual cycle, when estrogen production is at its peak, dry eye symptoms increase.6 Hormonal changes during pregnancy7 also worsen dry eye conditions.
- Post-menopause gives rise to a decrease in estrogen production which has been linked to poor functioning of the meibomian gland. This gland produces an oily substance called meibum which lies on top of the tear film and protects the tear film from rapid evaporation.8
- Other causes for dry eyes are smoking, drinking a lot of coffee, wearing contact lenses, being in air-conditioning or heated places with low humidity.
- Vitamin D deficiency is associated with eye pain, inadequate tear film, and unstable tear film according to 2015 and 2016 research.2, 3. 4
- Drugs that can cause dry eye symptoms See "Drugs That Harm the Eyes"
for a more complete list of harmful drugs which include:
- Appetite suppressants
- Birth control pills
- Blood pressure medications
- Over-the-counter drugs to "remove red" from eyes
- Ulcer medications
- Weather. Dry eye can also be triggered by dry windy weather and/or non-summer temperatures. Below 30° C (86° F) the outermost layer of the tear film, the oily meibum layer, is stiff and may not adequately cover and protect the tear film. When that happens the tear film evaporates very quickly.5
Diagnosis There are a number of tests used by eye doctors to find the source of problems - which layer of the tear film is involved:
- Schirmer tear test (commonly used in dry eye research)
- Tear film break-up time (10 seconds) (commonly used in dry eye research)
- Conjunctival impression cytology (commonly used in dry eye research)
- Rose Bengal staining pattern
- Tear Osmolarity
- Tear protein levels (lactoferrin and lysozyme)
- Presence of corneal filaments
- Evaluation of debris in tear film
How Your Eyes Stay Moist
The Mucous Membranes
The mucous layer is the innermost layer of the tear film, closest to the surface of the cornea. "Goblet cells," floating in the conjunctiva, are cells that are gland-like in that they produce mucin. Mucin interacts with the watery layer of the tear film to form the thin mucous layer of the tear film, which coats the cornea and allows for even distribution of the tear film. Goblet cells can be stimulated to greater production of mucin when the eye is irritated by environmental pollutants. Irritants such as some solvents can destroy goblet cells.
Eye surgery which holds the eyelids open can damage the conjunctiva and destroy goblet cells. This may be the reason so many patients experience severe dry eyes after eye surgery.
The Tear Glands
An aqueous layer (watery) makes up 90% of the thickness of the tear film. It is created by lacrimal glands, one for each eye, located behind the eyebrow. The slightly alkaline (pH-7.4) liquid produced by the lacrimal glands flows through canals into the lacrimal sac which is located on the inside of each eye beside the bridge of the nose. The action of blinking pumps tears onto and across the surface of the eye. In addition, tears flow from this sac into the nose - hence the reason you get a runny nose when there is too much fluid to stay on the surface of the eyes.
Nerves connect to the lacrimal glands, providing sensory stimulation (i.e., see what happens when you cut an onion) to stimulate tears. Blood vessels also connect to the lacrimal glands distributing nutrients and oxygen to the gland. These glands are also tied to the lymph system and as such help drain toxins and impurities from the surface of the eye.
A very thin lipid (oily) layer covers the outside of the tear film and helps slow evaporation of moisture. The Meibomian glands, located on the upper and lower eyelids between the eye lashes, secretes meibum. Meibum is also produced by the Zeis and Moll glands. Meibum is a sebaceous material, which is fluid at body temperature. It slows tear film evaporation and also lowers tear-film surface tension so that the tear film remains contoured to the surface of the eye and tears don't spill down to the cheeks. When the eyelids are closed, it is meibum which makes the eye within airtight.
The normal blinking process acts as a pump on the lacrimal sac to move more fluid to the eye and distribute it across the surface of the eye. Blinking is an essential part of eye comfort because the tear film naturally begins to degrade after about 10 seconds and needs renewal.
Dry Eyes News
Want to learn more? See our blog news on dry eyes.
Footnotes & Research
1. Dry Eyes and Migraines: Is There Really a Correlation? Cornea, June, 2012
2. Dry eye in vitamin D deficiency: more than an incidental association, 2015.
3. R. Shetty, et al, Corneal Dendritic Cell Density Is Associated with Subbasal Nerve Plexus Features, Ocular Surface Disease Index, and Serum Vitamin D in Evaporative Dry Eye Disease, BioMed Research International, February, 2016.
4. S.Y. Yoon, et al, Low Serum 25-Hydroxyvitamin D Levels Are Associated with Dry Eye Syndrome, PLoS One, January, 2016
5. I.A. Butovich, J.C. Arciniega, et al, Meibomian Lipid Films and the Impact of Temperature, Investigations in Ophthalmology and Visual Science, November, 2010
6. Menstrual Cycle Linked to Dry Eyes
7. Pregnancy and Dry Eye Syndrome
8. Dry eyes Linked to Meibomian Gland Dysfunction
See Dry Eyes Research.