What is dry eye syndrome? What causes dry eye syndrome?

Dry eye syndrome, also known as keratoconjunctivitis sicca (KCS), keratitis sicca, sicca syndrome, xerophthalmia, or simply dry eyes, is an eye disease in which tear film evaporation is high or tear production is low. Dry eye syndrome is commonly found in humans and some animals. The patient's eyes dry out and become inflamed. 

According to the National Health Service (NHS), UK, approximately between 17% and 30% of people have dry eyes at some time in their life. 

Our eyes are producing tears all the time, not just when we cry or experience a sudden rush of emotion or after yawning. Healthy eyes are covered with a fluid all the time, known as a tear film, which is designed to remain stable between each blink. A stable tear film prevents the eyes from becoming dry, and keeps the eyes clear, and with comfortable vision. 

If the tear glands produce a lower quantity of tears, the tear film can become destabilized. The tear film can break down quickly, creating dry spots on the surface of the eyes. 

Dry eye syndrome can occur at any age, and in people who are otherwise healthy. It is more common with older age, when the individual produces fewer tears. In some parts of the world, where malnutrition results in a vitamin A deficiency, dry eye syndrome is much more common.

What are the signs and symptoms of dry eye syndrome?

A symptom is something the patient feels and reports, while a sign is something other people, including a doctor or nurse may detect. For example, pain may be a symptom while a rash may be a sign. 

A patient with dry eye syndrome may have the following signs and symptoms:

• A stinging sensation in the eyes
• A burning sensation in the eyes
• Feeling of dryness in the eyes
• Feeling of grittiness and soreness in the eyes
• Stringy mucus in or around the eyes
• Eye sensitivity to smoke
• Eye sensitivity to wind (eyes water more in the wind)
• Redness of the eyes
• Eye fatigue, even after reading for a relatively short period
• Photophobia - sensitivity to light
• Discomfort when wearing contact lenses
• Tearing
• Blurred vision - usually worse towards the end of the day
• Double vision
• Eyelids stick together when waking up

Complications of dry eye syndrome may have the following signs and symptoms:

• Eye redness worsens
• Photophobia (light sensitivity) worsens
• Eyes become more painful
• Eyesight deteriorates

What are the causes of dry eye syndrome?

There are more to our tears than simply water. Tears are made of water, fatty oils, protein, electrolytes, substances to fight off bacteria, and growth factors. Tears are made of a mixture that helps keep the surface of our eyes smooth and clear. Without tears we cannot see properly. 

In some cases dry eyes are the result of an imbalance in the tear mixture, while in others not enough tears are produced for the requirements of good eye health. Other causes of dry eye syndrome include eyelid problems, some drugs, and environmental factors.

• Tear quality - the tear film has three layers - oil, water and mucus. If any of these layers are not right, the patient may develop dry eye symptoms.


• Oil (the top layer) - this oil is produced by the meibomian glands, located on the edge of the eyelids. They produce lipids (fatty oils). The oil smoothes the tear surface as well as slowing down the rate of evaporation. When oil levels are not right the tears may evaporate too rapidly. If a patient's meibomian glands are blocked (clogged) the likelihood of developing dry eyes is much greater. Patients with blepharitis (inflammation along the edge of the eyelids), rosacea and some other skin disorders have a greater risk of having clogged meibomian glands.


• Water (the middle layer) - this is the thickest layer, which consists of water and some salt. This layer is produced by the lacrimal glands (tear glands). They cleanse the eyes and wash away particles and irritants. If this layer is not right the patient is susceptible to film instability. If the water layer is too thin the oil and mucus layers may touch each other, resulting in a stringy discharge - a hallmark sign of dry eyes.


• Mucus (the inner layer) - this layer makes it possible for the tears to spread evenly over the surfaces of the eyes. If the mucus layer is not right, dry patches may develop on the cornea (the front surface of the eye).


• Reduced tear production - we tend to produce fewer tears after the age of 40 years. When tear production lowers to a certain point, the eyes can become dry and easily irritated and inflamed.
  
  Dry eyes caused by reduced tear production is more common among females than males; and especially more common among post-menopausal females. Experts say that this is due to hormonal changes.
  
  Reduced tear production is also linked to:
  
  
  • Inflammation
  • Radiation
  • Diabetes
  • Rheumatoid arthritis
  • Lupus
  • Scleroderma
  • Sjogren's syndrome
  • Vitamin A deficiency
  • Refractive eye surgeries, such as LASIK (laser-assisted in-situ keratomileusis). In such surgeries, the symptoms are usually temporary.


• Eyelid problems - each time we blink our eyelids spread a thin film of tears across the surface of the eyes. Most of us blink about five times a minute. If a patient has a problem with their eyelids, the blinking motion which evenly spreads the tear film may be affected. People with ectropion (eyelid turns outward) or entropion (eyelid turns inward) are examples of eyelid problems. Inflammation along the edge of the eyelids (blepharitis) may also cause dry eyes.


• Medications - the following prescription and OTC (over-the-counter, non-prescription) medications may also cause dry eyes:
  
  
  • Some diuretics
  • ACE (Angiotensin-converting enzyme) inhibitors
  • Antihistamines
  • Decongestants
  • Some sleeping pills
  • Birth control pills
  • Some antidepressants
  • Some acne drugs (isotretinoin-type medications)
  • Morphine and other opiate-based painkillers

The following may also cause dry eyes:

• Sun
• Wind
• High altitude
• A very dry climate
• Hot blowing air
• Very dry air (airplane cabin air)
• Working in front of a computer monitor (may slow down blinking rate)
• Driving a vehicle (may slow down blinking rate)
• Reading (may slow down blinking rate)
• Smoke
• Contact lenses
• Shingles
• Bell's palsy
• HIV

The examples above which are linked to a slowing down of blinking rate are usually because of intense visual concentration.

What is the Lacrimal Functional Unit?

Doctors and some other health care professionals use the term Lacrimal Functional Unit when referring to several body parts that work together in the production and regulation of tears. They include:

• The lacrimal gland - produces mainly water with a bit of salt. The main constituents of tears.


• The meibomian gland - produces a fatty liquid which is the outer layer of the tear film. Holds the tears in place and slows down evaporation.


• The eyelid - spreads tears evenly across the surface of the eye each time we blink.


• The cornea - a clear layer at the front of the eye. It contains smaller glands which produce liquids that make up our tears.


• The tear duct (lacrimal duct) - a small channel at the side of the eye that allows tears to run off into our nose.

Diagnosis of dry eye syndrome

Most GPs (general practitioners, primary care physicians) can diagnose dry eye syndrome from signs, asking the patient about symptoms and looking at the patient's medical history. The GP will need to know what medications the patient is currently taking, as well as information on their occupation and personal circumstances. 

The GP may refer the patient to an optometrist; a health care professional who is licensed to provide primary eye care services. With the aid of special devices the optometrist will be able to diagnose dry eye syndrome, as well as other conditions and possible complications, and offer treatment advice. 

The optometrist may carry out a number of tests, including:

• The Schirmer test - the aim here is to determine the quantity of tears behind the eyelid over a set period. Small strips of blotting-paper-like material are placed under the patient's eyelid. A few minutes later they are removed to see how wet they are.


• The Rose Bengal test - a Royal Bengal (a liquid stain, dye) is dropped onto the surface of the eye. The red dye helps the optometrist determine whether the tear film is functioning properly, as well as measuring the rate of tear evaporation.

The patient may be referred to an ophthalmologist if diagnosis is unclear, or if special tests and treatments are needed. An ophthalmologist is a doctor/surgeon who is specialized in diseases and treatments of eye conditions and diseases.

What are the treatment options for dry eye syndrome?

Treatment for dry eye syndrome depends on many factors, the main one being what is the underlying cause. The aim is to keep the eyes well lubricated.

• Eyelid problems - if the patient has something physically wrong with the eyelid, or an incomplete blink that causes dry eyes, the doctor may refer him/her to an oculoplastic surgeon - a surgeon specialized in eyelid problems.
  
  If the patient has blepharitis (inflammation of the eyelid) regular cleaning of the affected area with a dilute solution of baby shampoo may be recommended. The doctor may also prescribe antibiotic drops or ointment for night time use. The patient may alternatively be prescribed an oral antibiotic, such as tetracycline or doxycycline.


• Artificial tears - in mild dry eye cases the patient may find effective treatment simply by using OTC artificial tears. It is best to ask the doctor which ones are the most suitable.
  
  Eye drops without preservatives can be used at will, as many times a day as you like. Those with preservative usually have a maximum safe dosage of four times a day. Eye drops for removing redness should not be used.
  
  It may be a good idea to apply eye drops before activities which you know may exacerbate dry eye symptoms.
  
  Ointments are generally better for night time use, because they may blur vision.


• Keeping tears around for longer - tear ducts, which drain tears away, may be deliberately partially or completely blocked as a measure to conserve tears. Silicone plugs can be placed in the tear ducts to block them - they help keep your tears on your eyes for longer, as well as any artificial tears you apply.
  
  The doctor may apply a hot wire that shrinks the tissues of the drainage area, which closes the tear duct. This is called thermal cautery.
  
  Patients with severe symptoms are more likely to require silicone plugs, while those with mild symptoms may find that just using artificial tears are effective.


• Boston Scleral Lens - this contact lens rests on the sclera (the white part of the eye). It creates a fluid-filled layer over the cornea, preventing it from drying out.


• Medications - patients with chronic dry eyes may be prescribed cyclosporine (Restasis). Cyclosporine reduces eye-surface inflammation and triggers increased production of tears. Patients with an eye infection, as well as those with a history of herpes viral infection of the eye should not use this drug.
  
  Steroid drops may help reduce inflammation for patients whose symptoms remain severe, even after frequent use of eyedrops.
  
  Some studies indicate that omega-3 fatty acid consumption may help reduce the risk and/or incidence of dry eyes.


• Specialist eyewear - some patients benefit from wearing moisture chamber spectacles, which wrap around the eyes like goggles. The spectacles help retain moisture in the eyes, as well as protecting them from wind and other irritants. Moisture chamber spectacles are more popular than they used to be because of their current sporty designs. They used to have an unattractive design and were unpopular.


• Salivary gland transplantation - this surgical procedure is only ever considered in persistent and severe cases that have not responded to other treatments. Some of the salivary glands are removed from the lower lip and grafted, or placed into the side of the eyes. The saliva they produce becomes a substitute for tears.

Possible complications of dry eye syndrome

• Ulceration of the cornea - inflammation linked to severe and untreated cases of dry eye syndrome can damage the surface of the cornea, leading to ulceration (scarring). The patient's vision may become affected.


• Conjunctivitis - most conjunctivitis caused by dry eye require no treatment. Sometimes, however, conjunctivitis can become chronic (long-term or recurring) and severe. In such cases the patient should see a health care professional.


• Reflex tears - it is ironic that people with dry eye syndrome may sometimes produce too many tears. There are two types of tear production: 1. Basic tears; tears are produced at a slow and steady rate. 2. Reflex tears - tears are produced in large quantities in response to some irritant or emotion. Reflex tears have a much higher water content and a much lower mucus and oils content than do basic tears.
  
  When our eyes are irritated because of dryness, the lacrimal glands produce large quantities of reflex tears, which flood the tear ducts, resulting in overflowing eyelids. Because these tears have a different make up of water, oils and mucus, compared to basic tears, they do not help control dryness - they do not help keep the eye moist. So, the eye may react further and produce more reflex tears.
  
  The majority of people with dry eye syndrome experience no long-term problems or complications. Untreated dry eyes, especially if symptoms are more than mild, may result in eye inflammation, infection and damage to the surface of the cornea.

Prevention of dry eye syndrome

• Keep the eyes clean - people with clean eyes are less likely to develop blepharitis. Use warm/hot (not boiling) water, dab some cotton wool into it, and gently clean your eyes. Massage your eye gently with a clean finger in a circular motion - this will help move the mucus from the eyelid glands.


• Wind - wear wraparound glasses for protection from wind and hot air, which can cause dry eyes.


• Computer monitor - the monitor should be just below eye level.


• Avoid smoky places - if you smoke, give up. If you don't, avoid places where people smoke.


• Humidifier - a humidifier in the home will help moisten the air, which will help reduce the risk of dry eyes. Some people say that spraying curtains with a fine spray of water also helps keep the air humid.


• Nutrition - evidence is starting to appear indicating that a diet rich in omega-3 fatty acids may help prevent dry eye syndrome. Sources of omega-3 fats include salmon, trout, tuna, herring and sardines. If you are vegetarian/vegan, the following foods are rich in omega-3 fatty acids: canola oil, English walnuts, flax oil, ground flax seed, hemp oil, hemp seed, olive oil, pumpkin seeds, and soybeans.