What is Chronic Dry Eye?
Chronic dry eye, or simply “dry eye,” is a disease of the surface of the eye that can happen when your eye does not make enough tears or there is an issue with the tears that are made. Chronic dry eye may also be called dry eye syndrome (DES), dry eye disease (DED), or keratoconjunctivitis sicca.1
Who has chronic dry eye, and what causes it?
Recent studies have estimated that nearly 16.5 million adults in the United States have been diagnosed with chronic dry eye. Plus, there are about 6 million more people who have symptoms but have not been diagnosed.2
Chronic dry eye is thought to be caused by irritation or inflammation of the surface of the eye. This irritation occurs because the amount of lubrication on the eye is less than adequate.
Is ocular surface disease the same as chronic dry eye?
Ocular surface disease refers to any abnormality of the ocular surface (surface of the eye). This includes chronic dry eye, as well as many other conditions.3
Structure and function of the eye and tear film
To better understand chronic dry eye, a basic understanding of the eye and tear film helps. The tear film is the layer of fluid that covers the surface of the eye. This film is made up of 3 layers:4
- An oily (lipid) layer on the outside
- A watery (aqueous) layer in the middle
- A mucus (mucin) layer on the inside
Special cells known as goblet cells produce a protein called mucin, which is the building block for the mucus inner layer of the tear film. The glands of Krause and Wolfring in the eye make the middle, watery layer of the tear film. The lacrimal gland of the eye also secretes this layer of the tear film.5
The meibomian glands on the eyelids secrete the oily layer of the tear film. Tears drain from the ocular surface into tear ducts located on the inner corners of the eyelids and eventually into the nose.5
The cornea is a thin, clear dome-shaped tissue that covers the surface of the eye. The cornea serves 2 major purposes: protection and refraction (bending) of light for normal vision.6
How dry eye affects vision
The tear film and cornea are 2 important layers of the eye that light must pass through in order to achieve normal vision. Any abnormality of these structures, or any other structure of the eye, can affect vision.
Types and stages
There are different types and subtypes of chronic dry eye, as well as different levels of disease depending on the severity of symptoms. The condition is usually progressive, meaning that symptoms can worsen over time. Levels range from mild to severe.
Evaporative dry eye accounts for 85 percent of all cases of chronic dry eye. This type of dry eye may be caused by an insufficient oily tear layer, allowing tears to evaporate faster from the eye surface. This is usually caused by a dysfunction of the meibomian gland but can also be due to a number of other conditions.7
Aqueous deficient dry eye accounts for 10 percent of dry eye disease cases. This type occurs when there is decreased production of watery tear layer.7
Some people may have both evaporative and aqueous deficient dry eye. This is called mixed mechanism dry eye.8
Causes and risk factors
A number of inflammatory autoimmune disorders may cause chronic dry eye. Some of these conditions may include:1
- Sjogren’s syndrome
- Rheumatoid arthritis
- Thyroid disease
Certain medicines can also cause or contribute to chronic dry eye. Some of these may include:8
- Some allergy drugs (antihistamines)
- Certain antibiotics
- Sleeping aids
- Anti-anxiety drugs
- Heartburn drugs
- Acne drugs
- Drugs used to treat heart conditions
Older women have a greater risk for developing chronic dry eye. Additional risk factors may include environmental factors, like cigarette smoke and dry climate. Extended use of technology and screen time, wearing contact lenses, and certain laser vision correction procedures can also lead to chronic dry eye.8
Outcomes and complications
Chronic dry eye is a chronic, progressive disease. Prognosis, or chance of recovery, varies depending on the severity of the disease. Chronic dry eye may cause vision problems, but the disease does not cause blindness.
Mild complications may include blurred vision, light sensitivity, and the inability to wear contact lenses.
Severe complications from chronic dry eye are rare and usually occur due to an underlying condition beyond dry eye. In those with advanced disease, scarring of tissue or other eye issues may occur.8
Chronic dry eye is considered a chronic pain syndrome. Complications from chronic pain can include increased distress, anxiety, and depression in some people.