What Causes Dry Eyes?

Dry eye (medically coined keratoconjunctivitis sicca) is a condition of the eye that can be caused by several problems, including the inability to make enough tears, production of poor quality tears, or tears that evaporate too fast.

When tear production decreases or tears begin to evaporate too quickly, symptoms of dry eye can develop. These problems can occur due to a wide variety of underlying conditions and factors (such as a vitamin deficiency, hormone imbalances, aging, and more).

How Tears Work

To fully understand what causes dry eyes, it’s important to know some of the basics about how tears work. The physiology of tears is much more complex than one might initially think. Also, there is more than one type of tear, and all types are needed for healthy eyes.

Healthy tear production involves many different functions of the eye and associated structures, including:

• Sources of tears: Tears are constantly produced by glands located above the eyelids, such as the lacrimal glands, located just above each eye. Other sources of tears include a network of glands in the conjunctiva of the eye. These glands produce water and mucus. Also, there are glands near the lids of the eyes that produce an oily substance.
• Spreading of tears: Tears spread across the surface of the eye each time a person blinks.
• Types of tears: There are three different types of tears; each type has a different job when it comes to eye health. Some tears keep the eyes moist. Some wash away debris and lower the chance of infections in the eyes. Some tears are linked with emotions and are activated when a person cries.
• Tear makeup: The fluid that comprises tears is made up of moisture and oil to help keep the liquid tears from drying up. Tears contain mucus, which potentiates the even spreading of tears on the eye’s surface. The mucus layer also has antibodies to fight infectious organisms.
• Function of tears: Tears transport oxygen and nutrients to the surface cells of the eyes (because the corneas do not have blood vessels). Tears drain into small holes called the “puncta,” which are located in the corner of the eyes (in the upper and lower lids). Tears drain through the holes, then through tear ducts (very small channels that travel from the eyes to the nose).

Quality of Tears

Tears are normally comprised of three different layers, including:

• Oil layer: Prevents water from automatically evaporating into the air
• Water layer: Lubricates the eye and functions to wash away debris
• Mucus layer: Sometimes called the mucin layer; spreads the tears evenly over the entire surface of the eye

When there is a problem with any of the three layers of the eyes, such as when the tears evaporate too quickly or fail to spread evenly over the cornea (due to problems with any of the three layers), it can result in the development of dry eyes.

Tear Production

There are many reasons that a person’s process of tear production isn’t working properly. This includes:

• Aging: Tear production tends to diminish as a person gets older. This is due to decreased tear production, diminished corneal sensation, inflammatory destruction of lacrimal glands, and an increased risk of diseases that are known to cause dry eye, such as autoimmune diseases.
• Health conditions: Various health conditions are known to cause dry eye, including diabetes, thyroid dysfunction, autoimmune diseases, rheumatoid arthritis, Sjogren’s syndrome, lupus, Parkinson’s disease, ocular rosacea, vitamin A deficiency, hormone imbalance, and dehydration.
• Structural/anatomical changes: This could include trauma or surgery, like laser eye surgery or other refractive surgeries.
• Medications: Side effects of some medications, such as antihistamines, decongestants, antidepressants, and antihypertensives, can decrease the volume of tear production or cause an increase in tear evaporation. Even glaucoma eye drops or any eye drops that have preservatives can cause dry eye.

Note: It’s important to give your ophthalmologist a complete list of all medications you are taking, including prescriptions and over-the-counter (OTC) medications. Your ophthalmologist can help you identify medicines that could be causing your symptoms.

A Word From Verywell

If you think you may be suffering from dry eye, take the Cleveland Clinic’s self-test for dry eye disorder today to find out. This test is not meant to substitute for a visit to your eye doctor. Make sure to schedule an appointment for a medical consult and proper diagnosis.