What is the Leading Cause of Dry Eyes?
- As we age, the composition of eyelid bacteria tends to become imbalanced
- Excessive amounts of eyelid bacteria can damage the glands responsible for tear production
- Strategies that promote the balance of eyelid bacteria may help improve the quality of tear film
Dry eye is a common condition that results when the tear film is unable to adequately lubricate the eye surface. When the ocular surface becomes dry, it leads to eye inflammation and a number of unpleasant symptoms. If the symptoms of dry eye are not resolved, this can increase the likelihood of corneal abrasions (scratches of the eye surface) that may lead to an eye infection or reduce vision quality.
Symptoms of Dry Eye:
- Itchy, red, sore, or fatigued eyes
- Sense of pressure in eye
- Sensation of eye dryness, burning, or grittiness
- Heavy eyelids
- Excessive tearing
- Blurred vision
- Light sensitivity
Factors Affecting Tear Film
There are dozens of potential factors that can affect tear film quality, and it’s important to understand how each of these unique factors can affect the three components of tear film.
Tear film components:
| Tear Film Component | Layer | Gland or Cell | Main Function |
| Fatty oil (lipid) | Superficial thin layer | Meibomian glands | Responsible for the even spreading of tears |
| Watery (aqueous) | Middle thick layer | Lacrimal glands | Production of substances that have antimicrobial effects |
| Mucus (mucin) | Inner layer | Goblet & Epithelial Cells | To hydrate and lubricate the ocular surface |
Dry eye causes include:
| Cause | Consequences | Tear Component Affected |
| Aging | Lacrimal & Meibomian Gland Atrophy | Aqueous & Lipid |
| Autoimmune (Sjögren’s Syndrome) | Loss of Lacrimal Gland Function | Aqueous |
| Blepharitis | Loss of Meibomian Gland Function | Aqueous & Lipid |
| Blink Dysfunction | Increased tear film exposure | Aqueous & Lipid |
| Digital Screens (heavy use of phones, tablets, computers) | Increased tear film exposure | Aqueous & Lipid |
| Connective Tissue Disease (e.g., rheumatoid arthritis, lupus, scleroderma) | Loss of Lacrimal & Meibomian Gland Function | Aqueous & Lipid |
| Contact Lens Wear | Increase bacteria & may reduce goblet cell function | Mucin |
| Environmental Factors (e.g. chemical irritants from skincare products, smoke, pollution, blowing air from heating & cooling units) | Inflammation of multiple eye structures | Aqueous, Lipid, Mucin |
| Eye drops (with preservatives) | Toxic effects on eye epithelial cells | Aqueous, Lipid, Mucin |
| Medications such as: Antihistamines, Anticholinergics, Estrogens, Niacin, Selective Serotonin Receptor Antagonists | Alters Tear Flow Production | Aqueous Lipid Mucin |
| Meibomian Gland Dysfunction | Gland Inflammation and Loss of Function | Lipid |
What is the leading cause of dry eye?
Some ophthalmologists believe that dry eye is primarily caused by blepharitis, a common skin condition characterized by inflammation of the eyelids.1 Blepharitis is a condition that often occurs when the bacteria of the eyelid become overpopulated.2 If the supporters of this theory are correct, therapies that help maintain a healthy balance of eyelid bacteria may have the greatest potential for alleviating dry eye.
Imbalanced eyelid bacteria
The eyelids normally contain many types of bacteria, most of which are harmless or even beneficial.3 As we age, however, the bacteria along the eyelid margin (where the eyelashes are located) may become imbalanced, leading to the overpopulation of certain bacterial species.1 This is because the eyelid margins provide a warm, moist environment for bacteria to grow in a location that is particularly hard to clean. Over time, the increasing number of bacteria accelerates the buildup of biofilms (a glue-like substance similar to dental plaque or pond scum).4 Biofilms can be difficult to combat, given that their sticky surface allows bacteria to build up, and because they act like “layers of armor,” which makes it difficult for the body’s immune cells (or even antibiotics) to kill the bacteria.
Unfortunately, when eyelid bacteria become overpopulated, they can produce toxic substances that damage the tear glands.1 Because the meibomian glands are located along the eyelid margin, these glands are particularly vulnerable to getting “attacked” by bacterial toxins. Additionally, damaged meibomian glands produce abnormal oils that are toxic to the ocular surface.5 Conversely, healthy meibomian gland secretions hydrate the ocular surface and contain the antibacterial properties that promote a healthy balance of eyelid bacteria.
What’s more? The biofilms that build up along the eyelid margin can mix with other eyelid debris – blocking the gland openings and effectively preventing oils from reaching the surface.1,6 When the meibomian glands aren’t able to produce enough high-quality oils to comprise the outer layer of tear film, water quickly evaporates from the ocular surface. Ultimately, the lack of high-quality oils leads to a specific classification of dry eye known as evaporative dry eye disease.
Based on the current research, it’s certainly plausible that bacterial loads may be responsible for the loss of meibomian gland function.7 However, it’s also possible that meibomian gland dysfunction caused by aging and other factors may lead to increases in eyelid bacteria. In either case, treatments that target eyelid bacteria may increase the likelihood of providing relief for the millions of people who suffer from dry eyes.
Conclusion
Adequate hydration of the eyes is dependent on the production of high-quality oils. When chronically imbalanced, eyelid bacteria may damage the meibomian glands, impairing their capacity to deliver these critical oils to the ocular surface.
If you struggle with dry eyes, an eye doctor can evaluate whether you have excessive buildup of biofilms and imbalanced eyelid bacteria that may be linked to meibomian gland dysfunction – the most common cause of dry eye.
Antimicrobial Compounds that kill or limit the growth of microorganisms (eg. bacteria, virus, fungus).
Artificial tears: Over-the counter-eyedrops.
Biofilm: A strong protective barrier that allows bacteria to flourish.
Dry eye: A common condition that occurs when your eyelid glands are unable to produce quality tears.
Epithelial cell: The outer layer of cells that cover certain organs (such as the cornea of the eye) and blood vessels.
Evaporative dry eye: Dry eye resulting from abnormal meibomian gland function, and lack of fatty oil production.
Eyelid margin: The part of your eyelid where the eyelashes are located.
Goblet Cell: A cell responsible for the production of mucin (a gel-like substance that has cell-protective properties).
Lacrimal gland: Glands of the eye responsible for secreting the watery (aqueous) tear film component.
Meibomian gland: Glands located in the eyelids responsible for producing lipid-rich secretions that help the even spreading of tears.
Skin microbiome: A diverse array of bacteria, fungi, viruses, and certain other microorganisms that collineate the skin.
