Dry eye syndrome

Dry eye syndrome can have many different causes, including environmental factors, illnesses, side effects of medicines, hormonal changes, and ageing. However, in many cases, there is no one single identifiable cause.

The importance of tears

We often only notice our tears when something happens that makes us laugh or cry. However, our eyes are always covered by a thin layer of liquid, known as a tear film.

This liquid is made from of a mix of water, proteins, fats, mucus, and infection-fighting cells. Your tears serve several important functions:

• they lubricate your eye, keeping it clean, and free of dust,
• they protect your eye against infection, and
• they aid sight by helping to stabilise your vision.

Tears are produced and regulated by a system known as the lacrimal functional unit.

Lacrimal functional unit

The lacrimal functional unit is the name that healthcare professionals use to refer to the system of different parts of the body that work together to regulate the production of tears.

The lacrimal functional unit is made up of a number of different parts, which are described below.

• The lacrimal gland. This produces a liquid substance that makes up the majority of your tears.
• The meibomian gland. This produces a fatty liquid that makes up the outer layer of the tear film, that holds it in place.
• The eyelid. When you blink, your eyelid spreads tears across the surface of your eye.
• The cornea. The clear layer at the front of your eye that contains smaller glands, which also produce some of the liquid that makes up your tears.
• The tear ducts. Two small channels at the side of your eye that allow your tears to run off into your nose.

If any part of the lacrimal functional unit is affected, the whole system can break down. This can result in one of two outcomes, or possibly both. These are:

• the quantity of tears is affected, meaning that the body is not producing enough, and/or
• the quality of the tears is affected, meaning the tears evaporate before the body has a chance to replace them.

Either outcome can result in dry eye syndrome.

Also, as the eyes are no longer adequately protected by the tear film, the immune system (the body's natural defence system against infection) tries to compensate by sending special, infection-fighting cells to the eye. It is these cells that cause the inflammation of the eye associated with more serious cases of dry eye syndrome.

There are a number of things that can interfere with the lacrimal functional unit:

Hormones and the nervous system

Hormones and the nervous system can play an important part in tear production. Hormones help stimulate the production of tears. The changes that occur in hormone levels during the menopause may explain why older women are more susceptible to dry eye syndrome.

The nervous system can trigger an increase in tear production, often as a way of protecting your eyes from potentially harmful substances. This is why, for example, your eyes water if you are exposed to smoke.

Environment

Environmental factors can have a drying effect on your eyes, causing your tears to evaporate. These factors include:

• sun,
• wind,
• dry climate,
• hot blowing air, and
• high altitude.

Regular exposure to these environmental factors can cause dry eye syndrome. People are particularly at risk when they are exposed to a combination of factors. For example, the combination of a dry climate, and warm air conditioning, found in many offices, can cause dry eye syndrome in some people.

Occupation

When you are carrying out an activity that requires visual concentration, such as reading, writing, or working with a computer, you tend to blink less frequently. This can cause your tears to evaporate and lead to dry eye syndrome.

Medicines

There are several medicines that are thought to cause dry eye syndrome in some people. These include:

• antihistamines,
• antidepressants,
• beta-blockers, and
• diuretics.

Beta-blockers and diuretics are often used to treat high blood pressure (hypertension).

Laser surgery

Some people who have had laser-assisted in-situ keratomileuis (LASIK) surgery find that they experience dry eye syndrome in the weeks after surgery. However, the symptoms will usually clear up after a few months.

Contact lenses

In some people, contact lenses can irritate the eye and cause dry eye syndrome. Changing to a different type of lens, or limiting their use, will usually help to resolve the symptoms.

Menopause

In some women, the changes in hormones that occur during the menopause, can lead to a reduction in tear production, resulting in dry eye syndrome.

Medical conditions

Most people with dry eye syndrome also have blepharitis, inflammation of the rims of the eyelids. Blepharitis is commonly associated with:

• seborrhoeic dermatitis, a common skin condition that is often referred to as seborrhoeic eczema, and
• rosacea, a less common inflammatory skin condition that affects the face.

Other medical conditions that can cause dry eye syndrome in some people include:

• contact eczema, and
• conjunctivitis.

Less commonly, dry eye syndrome can be caused a number of other conditions which are outlined below.

• Sjögren's syndrome, a condition that causes excessive dryness of the eyes, mouth, and vagina.
• Rheumatoid arthritis.
• Lupus, a condition where your immune system attacks healthy tissue.
• Scleroderma, a skin condition that can also affect the blood vessels.
• Previous trauma, such as burns or exposure to radiation.
• Shingles, a nerve and skin infection caused by the herpes virus.
• Bell's palsy, a condition that affects the nerves in the face.
• HIV, Human Immunodeficiency Virus.

Aging

As we get older, we produce fewer tears. This, combined with the effects of the menopause, probably explains why dry eye syndrome is particularly common among older women.

Your GP should be able to diagnose dry eye syndrome by your symptoms and your medical history. An examination may be carried out to check for other conditions and complications.

They will also want to know about any medicines that you are taking, and your personal circumstances, in case a possible cause of your dry eye syndrome can be identified.

The Schirmer test

- in this test, small strips of blotting paper are placed under your eyelid. After five minutes, the strips are removed and studied in order to see how wet the paper is.

The Rose Bengal test

- in this test, a non-toxic dye, known as Rose Bengal, is dropped on the surface of your eye. The distinctive red colour of the dye allows the ophthalmologist to see how well your tear film is functioning, and how long it takes for your tears to evaporate.

Referral to an ophthalmolgist

If the diagnosis is uncertain, or specialist tests and treatment are required, your GP may refer you to an ophthalmologist. Ophthalmologists are surgeons who specialise in eye diseases and, like optometrists, they use special equipment and techniques, such as the Schirmer and Rose Bengal tests to examine the eye.

The symptoms of dry eye syndrome may include:

• feelings of dryness, grittiness, or soreness, in both your eyes, which get worse throughout the day,
• redness of your eyes,
• your eyes water, particularly when you are exposed to wind, and
• your eyelids stick together on waking.

Symptoms of complications

Dry eye syndrome can cause complications, such as scarring of your cornea (the transparent layer at the front of the eye) and conjunctivitis (inflammation, or infection, of your eye). Such complications can produce more severe symptoms, such as:

• you become extremely sensitive to light,
• your eyes become extremely red,
• your eyes are very painful,
• your vision starts to deteriorate.

You should not ignore the above symptoms because, left untreated, complications arising from dry eye syndrome could permanently affect your sight. See your GP as soon as possible.

Once dry eye syndrome develops, some people have recurring episodes for the rest of their lives.

Although no cure exists for dry eye syndrome, there are a range of treatments, such as eye drops, that can control your symptoms. Rarely, more severe cases of dry eye syndrome may require surgery.

Underlying medical conditions

If you have an underlying medical condition which is causing dry eye syndrome, your GP will prescribe treatment for it.

Most people with dry eye syndrome also have blepharitis, which is a common (and usually mild) chronic inflammation of the rims of the eyelids. The basis of treatment of blepharitis is eyelid hygiene. In other words, keeping the eyelids clean, and massaging any trapped material out of the glands in the rim of the eyelid.

If your underlying condition is a complex one, such as HIV, or lupus, you will need to be referred to a specialist for treatment, if you are not already receiving treatment for the condition.

To treat your dry eye syndrome, the specialist will be able to address, and then try to eliminate, any possible triggers of the condition, such as medicines, or environmental factors. Different types of medicines can be prescribed.

It is also possible to make changes to compensate for environmental factors - for example, placing a humidifier in your home, or workplace, may help to reduce dryness.

You may also be recommended to change your work habits. For example, if you job involves a lot of computer work, taking breaks every hour to rest your eyes, may help to reduce your symptoms.

If these measures are not successful, other treatments, which are described below, can be tried.

Tear substitutes

Mild to moderate cases of dry eye syndrome can normally be successfully treated with eye drops that contain 'tear substitutes', a liquid that is designed to mimic the properties of tears. These eye drops are available from a pharmacy over-the-counter (OTC) without prescription.

There are many different types of eye drops, so you can try a different type if your original choice proves ineffective.

Some eye drops contain a preservative which helps prevent evaporation. It is probably best to avoid using eye drops that you have to use frequently (more than six times a day) because these sorts of eye drops contain a preservative that can sometimes irritate the eye. Your GP or pharmacist will be able to advise you about an alternative.

Ointment can also be used to help lubricate your eyes. However, it can often cause blurred vision, so it is probably best to use it last thing at night.

Anti-inflammatory medicine

Anti-inflammatory medicines can be used to help reduce the inflammation associated with more severe cases of dry eye syndrome. They work by blocking the functions of your immune system that are involved in triggering inflammation.

Anti-inflammatory medicines are normally prescribed in the form of a cream or ointment.

Specialised eyeware

Some cases of dry eye syndrome can be treated using specialist eyeware. These include specially made glasses, known as moisture chamber spectacles. These wrap around your eyes like goggles, helping to retain moisture and protecting your eyes from irritants.

Moisture chamber spectacles used to be unpopular because they had a strange looking design, and people were embarrassed to wear them. However, they are now becoming a more popular treatment option because the modern designs look just like sports sunglasses.

If your previous contact lenses were causing dry eye syndrome, specially designed contact lenses are also available.

Surgery

If your dry eyes fail to respond to other forms of treatment, surgery may be an option.

One surgical technique, known as punctual occlusion, involves using small plugs to seal your tear ducts, which help keep your eye protected by tears. Temporary plugs made of silicone are normally used first to see if the operation has a positive effect. If it does, more permanent plugs can be used to replace the silicone ones.

Another surgical technique for treating very severe dry eye syndrome is known as salivary gland autotransplantation. This procedure is normally only recommended after all other treatment options have been tried.

Salivary gland autotransplantation involves some of the glands that produce saliva being removed from your lower lip and placed, or grafted, into the side of your eyes. The saliva that is produced by the glands acts as a substitute for tears.