The Composition of Tears and Their Role in Eye Health

Your tears obviously are made of water with some salt, as you've tasted when you've had a good cry. But are there other ingredients in tears? Are some tears different from others?

Tears are produced in the lacrimal glands (tear ducts) that are in the outer corners of your eyelids. These glands produce tears from your blood plasma, selecting some components but not others. The basic components of tears are:

• Water
• Electrolytes (sodium, potassium, chloride, bicarbonate, magnesium, and calcium). These are what give tears their salty taste.
• Proteins (lysozyme, lactoferrin, lipocalin, and IgA). The tears have only about one-tenth of the protein of the blood plasma.
• Lipids
• Mucins

Tears play an important role in keeping us healthy. Tears keep the surface of our eyeballs clean and moist and help protect our eyes from damage. Although they make appear to be nothing more than water, our tears are actually quite complex. Tears are made of mucus, water, and oil and each plays a role in the eye.

• Mucus coats the surface of the eye and helps bind the tear layer to the eye. Without a healthy mucus layer, dry spots may form on the cornea, the clear dome-like structure on the front of the eye.
• The water is really more of a saline (salt) solution that contains various vitamins and minerals vital to normal cell function. These nutrients are important for keeping the top layer of cells on the surface of the eye, the epithelium, healthy and functioning normally.
• The oil of the tear film prevents evaporation of the tears. Some people don't make enough oil (or sometimes too much oil), resulting in dry eyes. If the oil component is not normal, the tears evaporate too quickly.

Our tears also contain natural antibiotics called lysozymes. Lysozymes help to keep the surface of the eye healthy by fighting off bacteria and viruses. Because the cornea has no blood vessels, the tears also provide a means of bringing nutrients to its cells.

When your eye is irritated, it produces reflex tears to wash out the irritants. You've probably shed a few tears when chopping onions or when you get dust in your eyes.

The tears you shed when overcome with emotions have a higher protein content than the tears shed from irritants. In a classic experiment, a researcher found that emotional tears had more hormones, including prolactin, adrenocorticotropic hormone, and leucine enkephalin.

When you sleep, your tear ducts add less water and protein to your tears but they increase the number of antibodies, and infection-fighting cells also migrate to the conjunctival sac.

As you age, you usually produce fewer tears by volume, and this can lead to developing dry eyes. The proteins your lacrimal ducts normally add to tears decreases.