What is Dry Eye Disease?
"Dry eye," is a broad term used to describe a variety of conditions that are commonly the result of inadequate lubrication of the front of the eye. This inadequate lubrication is frequently caused by the overproduction, underproduction, or unhealthy production in the tear film's three layers.
What is the tear film?
The front of the eye is always covered in a thin, three layered coat of tears called the tear film. The tear film's three layers comprise:
- Lipid layer - the outermost layer of the tear film, the oily lipid layer lubricates the eye evenly and prevents the evaporation of the underlying layers. This layer is produced by the Meibomian Glands which are located in the upper and lower eyelids.
- Aqueous layer - the middle layer of the tear film, the watery aqueous layer nourishes and protects the eye. The aqueous layer is produced by the Lacrimal Glands which are found in the upper eyelids.
- Mucin layer - the innermost layer of the tear film, the sticky mucinous layer serves to adhere the other layers to the front of the eye. The mucinous layer is produced by Goblet Cells that are located throughout the front of the eye.
Why do we have tears?
There are two kinds of tears: those that lubricate the eye and those that are produced as a response to irritation or emotion. Tears that lubricate the eye are produced round the clock. Excessive tearing occurs due to emotional response or if an eye is irritated by a foreign body.
Although tears flow when we cry or when our eyes are irritated, our tears have a much more important, everyday function. The tear film, spread over the ocular surface during each blink, makes the eye's surface smooth and optically clear, washes away foreign particles and irritants, keeps the eye moist and hydrated, and provides valuable nutrients that feed the ocular surface. Without the tear film, good vision would not be possible.
What is causing my dryness?
Dry eye diseases and conditions commonly occur due to an imbalance among the three layers of the tear film. Although dry eyes can occur in both men and women of any age, tear production is typically age related: elderly individuals more commonly report symptoms of dryness and irritation. Additionally, post menopausal women are more often affected than men. Other factors that can contribute to such an imbalance include smoke, pollution, extreme heat or cold, windy environments, and concentrated reading or computer use for extended periods of time. Aside from these environmental factors, systemic factors like allergies, hormonal changes or health status such as diabetes, thyroid dysfunction, autoimmune diseases including Sjogren's Syndrome, Lupus or Rheumatoid Arthritis, and certain types of medications including antihistamines, anti-depressants and hormone replacement can increase dry eye symptoms.
What are the symptoms of dry eyes?
Symptoms of dry eye include dryness, scratchiness, burning or stinging, a foreign body sensation, grittiness, fluctuating blurred vision, redness, general discomfort, sensitivity to light, contact lens discomfort, and tear debris. Patients with dry eyes often complain that their eyes feel tired, itchy and irritated. Patients may experience their eyelids sticking together in the morning and have difficulty wearing contact lenses. Surprisingly, watering eyes is also a symptom of dry eyes as excess tears are produced in response to irritation. However, this kind of tear which consists mostly of water and cannot adequately rehydrate the eye. Excess tears lack the oil necessary to keep them from evaporating and lubricating the eye. While discomfort is the primary result of dry eyes, infection and visually impairing corneal scarring may occur if the dryness remains untreated.
How are dry eyes diagnosed?
Often, ocular surface diseases and conditions are detected during a routine eye examination. Sometimes tests that measure tear production may be necessary. Various tests that aid in the diagnosis and treatment of dry eye conditions include Tear Lab Osmolarity, Inflammadry, the OSDI/SPEED score, and temporary corneal staining.
- It has been estimated that 10 to 20 percent of the U.S. population suffers from dry eye. Nearly six million women and three million men in the U.S. have moderate or severe symptoms of the condition. Scientists estimate that an additional 20 to 30 million people in this country have mild cases of dry eye.1
- It is estimated that the rate of diagnosis of dry eye is low “ at approximately five percent.2 Dry eye conditions can be difficult to diagnose because there are so many possible causes and contributors. Also, not everyone experiences or describes symptoms in the same way.
For more information about the treatment of Dry Eye, go to Treatment for Dry Eye.
1Eye Disease Information and Resources: Dry Eye Fact Sheet. The Schepens Eye Research Institute. 2003.
2Lemp MA, on behalf of Alcon Laboratories. Systane®: A Therapeutic Option for Dry Eye.