Dry Eye CausesDry Eye Treatment

How Do Tears Work?

By September 2, 2022 November 7th, 2023 No Comments
photo of an eye up close - how do tears work?

Tears perform many critical functions for your eyes. They ensure your eyes remain adequately lubricated and help focus light so you can see clearly. Tears protect your eyes from infections and irritants by flushing away dirt and dust.

When you blink, a thin layer of tears, called the “tear film,” spreads across the outer surface of your eyes (cornea) to lubricate. Tears originate in the glands above your eyes and drain into the tear ducts in your eyes’ inner corners. However, a common condition called dry eye disease can occur when your tears dry too quickly, or your eyes don’t make enough.

The Three Layers of the Tear Film

Three layers comprise the tear film. Each layer plays a role in maintaining eye moisture levels and ensuring comfort. If any component fails to perform its function, the tear film can’t properly coat your eyes, and dryness arises.

The layers and their functions are as follows:

Lipid Layer

The lipid (oil) layer is the outermost component of the tear film and works to stabilize it. When the tear film contains less oil, your tears evaporate too quickly, resulting in Meibomian Gland Dysfunction. This dysfunction is the most common cause of dry eye syndrome.

Aqueous Layer

The aqueous layer comprises the largest portion of the tear film. Its primary responsibility is supplying the moisture needed to ensure comfort. When your eyes don’t produce enough water, Aqueous Layer Deficiency occurs, and your eyes struggle to retain moisture.

Mucin Layer

The mucin layer consists of proteins (called mucins) that coat the eye. As the innermost layer, mucins allow the aqueous moisture to spread across the otherwise water-repellant cornea.

a blue eye - how do tears work?

What Causes Decreased Tear Production?

Two common causes of dry eye disease include decreased tear production from an error in the aqueous layer and increased tear evaporation from inadequacies in the lipid layer. Certain factors can lower the aqueous layer’s ability to produce sufficient moisture for your eyes, such as:

  • Aging
  • Certain medical conditions, such as Sjogren’s syndrome, rheumatoid arthritis, lupus, allergic eye disease, or thyroid disorders
  • Certain medications, such as decongestants, antihistamines, antidepressants, birth control, hormone replacement therapy, and prescriptions for acne, high blood pressure, or Parkinson’s disease
  • Excessive contact lens wear, causing corneal nerve sensitivity

Most people with occasional or mild dry eye symptoms feel relief from over-the-counter eye drops. However, those with worsening symptoms should visit their optometrist for testing that can help identify the underlying cause.


Those who experience dry eye symptoms from decreased tear production can benefit from certain medications and procedures. For instance, a group of cholinergic medications can help increase tear production. These tear-stimulating medications are available as gels, pills, or eye drops.

Patients can also experience relief from procedures such as punctal plugs, the process of closing the tear ducts to maintain fluid levels. Also, special contact lenses protect the cornea and trap moisture, thus prompting the eyes to produce more tears. Each treatment method aims to increase tear production.

What Causes Increased Tear Evaporation?

When the Meibomian glands, the structures producing oils in the tear film’s lipid layer, become clogged, tear evaporation occurs. Certain factors increase the clogging and tear evaporation, such as:

  • Meibomian Gland Dysfunction
  • Eye allergies
  • Eyelid problems
  • Wind, smoke, or dry air
  • Blinking less often as a result of prolonged reading, driving, or screen use
  • Preservatives in topical eye drops


When your optometrist identifies the underlying cause of your symptoms as increased tear evaporation, medications and other treatment methods can provide relief. For example, when the edge of your eyelids becomes inflamed, the oil glands may not secrete enough oil into tears, thus increasing the risk of evaporation. Certain medications aimed at reducing inflammation can prevent dryness.

Corneal inflammation may also create dry eye symptoms when oil cannot spread across the surface. The poor quality of tears causes the aqueous moisture to evaporate. Medications such as cyclosporine (Restasis) or corticosteroids can suppress inflammation.

Relief is Possible at the Dry Eye Institute of St. Louis

The doctors at the Dry Eye Institute of St. Louis specialize in diagnosing and treating dry eye disease. At our dry eye treatment center, we seek to discover the underlying cause of your symptoms using the latest specialized testing tools and equipment, then treat you accordingly. Our dry eye specialists have early access to new medications and treatments, so you can rest assured that the care you receive is unique to your needs.

Don’t hesitate to schedule an appointment with Dr. Bourn or Dr. Weis of the Dry Eye Institute today for specialized testing and relief!


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