A sad movie or a wedding can make your tears flow. But tears aren't
produced only on those occasions. Healthy eyes are continuously covered by a tear film — a constant layer of fluid designed to remain stable between blinks. A stable tear film prevents dry eyes and allows your eyes to maintain clear, comfortable vision.
The tear film protects your eyes and lubricates them. It also reduces the risk of eye infection and, with each blink of your eyelids, helps clear your eyes of any debris. When your eyes become irritated by dust or are bothered by wind, smoke or fumes, extra tears form to help wash away the foreign material.
Decreased production of fluids from your tear glands can destabilize the tear film, allowing it to break down rapidly and create dry spots on the clear front surface of the eye (cornea) that cause irritation and diminished vision. An imbalance in the substances that make up the tear film also lead to dry eyes.
Dry eyes are a common source of discomfort, and usually dry eyes are a chronic problem. Adults age 40 or older are most likely to experience dry eyes. Treatment of dry eyes is aimed at restoring a more normal tear film to minimize dryness and its consequences, including blurred vision and discomfort.
Signs and symptoms
Signs and symptoms of dry eyes may include:
A stinging, burning or scratchy sensation in your eyes .
A sense of a foreign substance in your eyes .
Stringy mucus in or around your eyes .
Increased eye irritation from smoke or wind.
Eye fatigue after short periods of reading.
Sensitivity to light.
Difficulty wearing contact lenses.
Blurred vision, often worsening at the end of the day or after visually focusing for a prolonged period on a nearby task.
Both eyes usually are affected.
Causes
Tears are much more than just water. They're a complex mixture of water, fatty oils, proteins, electrolytes, bacteria-fighting substances and growth factors that regulate various cell processes. This mixture helps make the surface of your eyes smooth and clear. Without tears, good vision is impossible.
For some people, the cause of dry eyes is an imbalance in the composition of their tears. Other people don't produce enough tears to keep their eyes comfortably lubricated. Eyelid problems, medications and other causes, such as environmental factors, also can lead to dry eyes.
Poor tear quality
The tear film has three basic layers: oil, water and mucus. Problems with any of these layers can cause dry eye symptoms.
Oil
The outer layer, produced by small glands on the edge of your eyelids (meibomian glands), contains fatty oils called lipids. These smooth the tear surface and slow evaporation of the middle watery layer. When the oil layer is abnormal, the watery layer evaporates too quickly. Dry eye problems are common in people whose meibomian glands are clogged. Meibomian dysfunction is more common in people with inflammation along the edge of their eyelids (blepharitis), rosacea and other skin disorders.
Water
The middle layer, which makes up about 90 percent of tears, is mostly water with a little bit of salt. This layer, produced by the tear glands (lacrimal glands), cleanses your eyes and washes away foreign particles or irritants. A shallow water layer can predispose you to tear film instability. If your eye produces only small, inadequate amounts of water, the oil and mucus layers can touch and cause the stringy discharge familiar to people with dry eyes.
Mucus
The inner layer of mucus allows tears to spread evenly over the surface of your eyes. Dry spots form easily in any part of the cornea that has patchy loss of the mucus layer.
Decreased tear production
Tear production tends to diminish as you get older. When you're unable to produce enough tears, your eyes become dry and easily irritated. The medical term for this condition is keratoconjunctivitis sicca (ker-uh-to-kun-junk-ti-VIE-tis sik-uh).
Although dry eyes can affect both men and women at any age, the condition is more common among women, especially after menopause. This may be due in part to hormonal changes. Damage to the tear glands from inflammation or radiation can hamper tear production. Dry eyes are also associated with medical conditions such as diabetes, rheumatoid arthritis, lupus, scleroderma and Sjogren's syndrome.
Refractive eye surgeries such as laser-assisted in-situ keratomileusis (LASIK) also may cause decreased tear production and dry eyes. Symptoms of dry eyes related to these procedures usually resolve after several months.
Poor lid function
Through blinking — normally at a rate of about 13 blinks each minute — your eyelids spread a continuous thin film of tears across the surface of your eyes. Problems with your eyelids can impair the complex blinking motion required to spread these tears, resulting in dry eyes. Eyelid problems that may develop as you age include an out-turning of the lids (ectropion) or an in-turning of the lids (entropion).
Blepharitis, an inflammation along the edge of the eyelids, also may cause your eyes to feel dry and scratchy.
Medications
The types of common medications, both prescription and over-the-counter (OTC), that can cause dry eyes include:
Diuretics, drugs commonly used to treat high blood pressure
Antihistamines and decongestants
Sleeping pills
Birth control pills
Tricyclic antidepressants
Isotretinoin-type drugs for treatment of acne
Opiate-based pain relievers such as morphine
Other causes of dry eyes
Dry eyes can be worsened by exposure to many environmental conditions that have a drying effect, such as sun, wind, high altitude, a dry climate, hot blowing air and the dry air that commonly occurs in the cabins of commercial airplanes.
In addition, tasks that require intense visual concentration — such as working at a computer, driving or reading — tend to decrease your blink rate, thereby increasing tear evaporation.
In some people, the cause of dry eyes is an allergic reaction to eyedrops or ointments.
When to seek medical advice
Although dry eyes don't usually cause permanent damage, diminished vision may prompt you to seek medical treatment.
See your doctor if you've had prolonged signs and symptoms of dry eyes, including red, irritated, tired or painful eyes. Your doctor can take steps to determine what's bothering your eyes or refer you to a specialist.
Complications
It sounds like a contradiction, but you may have dry eyes and still at times find yourself with tears streaming down your cheeks. Why?
Production of tears occurs in two ways. Basic tearing produces tears at a slow, steady rate and keeps your eyes lubricated. What's called reflex tearing produces large quantities of tears in response to eye irritation or emotions. Reflex tears contain much more water than do basic tears, and they're low in mucus and oils.
When your eyes become irritated from dryness, the lacrimal glands flood your eyes with reflex tears. Fluid overwhelms the tear ducts and overflows your eyelids. What's more, because these tears are of poor quality, they don't help the dryness. That may make you produce even more tears.
Most people with dry eyes don't experience any long-term complications. However, if left untreated, severe dry eyes may lead to eye inflammation, infection and scarring on the surface of your cornea.
Treatment
Effective treatment begins with a careful examination to determine which factors may be causing your symptoms. The goal of treatment is to keep your eyes moist.
Managing lid problems
If you have an eyelid condition, such as an anatomic abnormality or an incomplete blink that aggravates your dry eyes, your doctor may refer you to an eye surgeon who specializes in plastic surgery of the eyelids (oculoplastic surgeon). If your eyelids are inflamed due to blepharitis, your doctor may recommend regular cleaning of the area with a dilute solution of baby shampoo. Your doctor also may prescribe short-term, nightly treatment with antibiotic drops or ointment or treatment with an oral antibiotic such as tetracycline or doxycycline.
Adding tears
You can usually treat a mild case of dry eyes with over-the-counter artificial tears. Your doctor or eye doctor can suggest which drops might be best for you. You can use the lubricating drops as often as you need, even several times an hour, to provide relief. Using drops proactively, before you begin an activity that tends to aggravate your symptoms, also helps. If you use drops frequently, preservative-free eyedrops might be the best choice to avoid an allergic or toxic reaction to preservatives. You can also use ointments to ensure lubrication. These ointments can blur vision, so it's best to use them only at bedtime.
Conserving tears
Your eye doctor may also suggest methods to keep your natural tears around longer. This can be done by partially or completely closing your tear ducts, which normally serve to drain tears away. The tear ducts can be plugged with tiny silicone plugs. The closure conserves both your own tears and artificial tears you may have added. Silicone plugs can be removed or left in. A more permanent option is thermal cautery. In this procedure your doctor numbs the area with an anesthetic and then applies a hot wire that shrinks the tissues of the drainage area and causes scarring, which closes the tear duct.
People with mild dry eyes respond well to treatment with artificial tears. Some people have persistent symptoms and don't respond to artificial tears alone even though their eyes appear fairly normal. Severe dry eyes require more aggressive treatment, such as the silicone plugs. People with severe dry eyes also may benefit from a special customized contact lens (Boston Scleral Lens). This lens rests on the white part of the eye (sclera), creating a fluid-filled layer over the cornea that keeps it from drying out.
It's possible that more than one variable may be contributing to your signs and symptoms. Together with your doctor, you can devise a plan to address the factors that appear to be contributing to the problem. This process often takes time and requires patience and a trusting relationship with your doctor.
When dry eyes don't respond to artificial tears alone, some people may worry that they have an autoimmune disease, such as Sjogren's syndrome. While many people with autoimmune diseases have dry eyes, the large majority of people with dry eyes don't have autoimmune problems.
MedicationsYour doctor may prescribe cyclosporine (Restasis), the only medication approved by the Food and Drug Administration (FDA) for chronic dry eyes. Restasis decreases inflammation on the eye surface and helps increase production of healthy tears. Some people experience a burning sensation in their eyes when using this drug. Don't use Restasis if you currently have an eye infection or if you have a history of herpes viral infection of your eye.
When people experience intolerable irritation from dry eyes despite the frequent use of lubricating eyedrops, doctors may prescribe steroid drops.
Unconfirmed evidence suggests that high dietary intake of omega-3 fatty acids may lower the risk of dry eyes. Although this has led some people to use omega-3 dietary supplements, the effectiveness of this approach hasn't been proved.
Self-care
Like any liquid, tears will evaporate when exposed to air. You can take these simple steps to help slow evaporation:
Avoid air blowing in your eyes. Don't direct hair dryers, car heaters, air conditioners or fans toward your eyes.
Wear glasses on windy days and goggles while swimming. The wraparound style of glasses may help reduce the effects of the wind.
Keep your home humidity between 30 percent and 50 percent. In winter, a humidifier can add moisture to dry indoor air. Some people use specially designed glasses that form a moisture chamber around the eye, creating additional humidity.
Avoid rubbing your eyes. You can irritate your eyes further by rubbing them.
Take preventive steps. Use eyedrops before, rather than after, your eyes become irritated as a result of visually demanding activities. Try to avoid activities that might worsen the problem.
Remember to blink. Consciously blinking repeatedly helps spread your own tears more evenly.
When performing tasks that require intense visual concentration, take occasional breaks — adding up to about five minutes each hour — and rest your eyes by closing your lids for several seconds. Follow this by consciously increasing your blink rate. Be especially careful to follow these suggestions if you have had LASIK or a similar procedure
Adapted from: Mayo Foundation for Medical Education and Research
