The term "dry eye" seems pretty straightforward, right? The medical term for the disorder, however, is keratoconjunctivitis sicca. Which means that the condition is characterized by inflammation of the mucous membranes of the eye and dryness of the eye's corneal surface.
Causes of Dry Eye
What causes dry eye? Several factors combine to cause the condition. Thus we call it a multifactorial ("many factors") disorder.
The human eye needs adequate hydration in order to function properly. The transparent outermost surface of the eye--the cornea--is a durable yet thin structure only six or seven cell layers deep. The tear film that covers it sweeps away foreign particles and invading organisms, acts as a barrier, contains fatty acids and proteins that nourish the cornea, and furnishes immune system components that help protect the eye. If too little tear film is produced, or if it has an abnormal composition, is not adequately distributed, or evaporates too quickly, the cornea may be damaged.
Let's take a closer look at these contributing factors:
- The eye doesn't produce enough tears to keep its exposed surface moist. If the cornea dries out, it can ulcerate (break down and become scratched), giving bacteria, viruses, and other harmful organisms tiny hiding places in which to multiply.
- The composition of the tears is abnormal. If you've ever tasted your own tears, you know that they're not just made up of water--they also contain sodium, making them taste salty, and many other components. If the proportions of these components change, the tear film won't function effectively.
- The tear film evaporates too quickly. Glands along the edges of the eyelids produce oil, which slows the rate at which the tear film evaporates. If these glands become inflamed or infected, they may produce too little oil.
- The eyelids are unable to distribute the tear film evenly over the eye's surface. The eyelids may be droopy, a condition called eyelid ptosis, so that the person is unable to close the eyes properly or blink normally. Or the tear film may not contain enough mucus to distribute the tears evenly.
Signs and Symptoms
Dry eye can cause more than just discomfort. In severe cases, the cornea can perforate (detach), resulting in low vision and perhaps making a corneal transplant necessary. Signs and symptoms of dry eye include the following:
- A gritty, scratchy sensation, as if you have sand in your eyes
- Watery eyes, especially when reading or watching television
- Stinging, burning, or itchy eyes
- Inability to wear contact lenses for an extended period of time (or inability to wear them at all)
- Stringy mucus around the eyes and eyelids
- Visual disturbances, such as blurred or double vision
Certain people are more vulnerable to dry eye than others. Women, for example--especially after menopause, develop the condition more often than men do. In addition, certain disorders that affect other parts of the body, such as the skin and joints, are characteristically accompanied by dry eye:
- Autoimmune diseases such as rheumatoid arthritis, lupus, and scleroderma.
- Ocular rosacea
- Herpes zoster (shingles)
General risk factors for dry eye include the following:
- Advancing age (especially after menopause in women)
- Eyelid inflammation or drooping
- Exposure to cigarette smoke (your own or second-hand smoke)
- Exposure to wind during outdoor activities
- Exposure to radiation
- Exposure to dry air caused by using a central heating system, traveling on an airplane, or living in an arid climate
- Vitamin A deficiency
- Wearing contact lenses
- Watching television, reading, driving, or using a computer for long stretches
- Taking certain medications, such as isotretinoin (Accutane and others), decongestants, and diuretics
Your family doctor or eye care provider can diagnose dry eye by asking you about your symptoms and examining your eyes, often with the help of a dye administered using eye drops. Sometimes the provider performs a Schirmer test, using specially treated paper to determine how much tear film your eyes are producing.
Treating dry eye effectively usually requires a three-part strategy:
- Replenishing tear film. Tears can be supplemented with over-the-counter or prescription eye drops. Prescription drops actually encourage your eyes to produce more tear film.
- Retaining tears. Tiny silicone plugs can be used to slow the rate at which tears drain from the eyes. Another option is to keep tears from evaporating by using special contact lenses that cover the entire eye or by wearing specially designed, goggle-like eyeglasses that create a chamber of humidity around the eye.
- Treating underlying problems. For example, infection of the eyelid glands can be treated by applying antibiotic ointment and following modified hygiene practices.
Despite having a multifaceted cause that often calls for multi-pronged treatment, dry eye can be prevented or its severity reduced by taking the following commonsense steps:
- Keep your environment as moist as possible; use a room humidifier if necessary.
- Stay out of the wind or protect your eyes during outdoor activities.
- Avoid smoke, radiation exposure, and other triggers of dry eye, including excessive use of decongestants and other medications that have a drying effect.
- Quit smoking if you smoke cigarettes or other tobacco products.
- If you have diabetes, follow your doctor's instructions for controlling your blood sugar and making lifestyle modifications to improve your symptoms.
- Follow a diet low in saturated fat (such as the fat found in ice cream and most fried foods) but high in omega-3 fatty acids (the kind of fat found in fish, canola oil, kidney beans, and walnuts).
- Remember to blink frequently when driving, cueing up a YouTube video, watching Desperate Housewives, or curling up with a good H.L. Mencken novel.