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Dry eye

What Is The Tear Film?

The eye and eyelids are lined by a fluid layer called the tear film. This is so fine as to be nearly invisible – It can just be seen as a sheen on the eye surface. A healthy tear film is essential it contains antibacterial agents, lubricates the eye surface and provides it with oxygen and nourishment. The tear film is not a simple layer of water but a complex mixture of water, lipids (oils), mucous and proteins. The lacrimal glands (located behind the eye) produce the water and antibacterial agents, the meibomium glands (located in the eyelids) produce the lipids and numerous cells distributed on the eye surface produce the mucous. The tear film is not static. In fact it is constantly being renewed, spread around the eye surface by the action of blinking and discharged into the tear ducts. The opening of the tear ducts are on the inner corner of the eyelids (the same side as the nose) and can just be seen as minute dots.

What Is Dry Eye?

In a broad sense, ‘dry eye’ is caused by reduced production of any of the different components of the tear film. However when ophthalmologists (eye doctors) use the term ‘dry eye’ they are usually referring to a specific insufficiency of the water component of the tear film, produced by the lacrimal gland. It is this specific problem, namely deficiency of the water component of the tear film, that is discussed here.

The Symptoms Of Dry Eye

The symptoms include eye discomfort, redness, grittiness and even pain. Patients often complain of ‘tired eyes’. Vision may be intermittently blurred. Symptoms may be worse when reading or watching TV because the rate of blinking is less during these visual tasks. Air conditioned and smoky environments exacerbate eye dryness. Some patients also suffer from a dry mouth (see below).

Dry eye is a common problem, some studies estimating it affects 1%-2% of the population.

The Cause Of Dry Eye

The common causes of dry eye are. 1. Age related. Water production by the lacrimal gland often decreases in older persons. It is now known that in both men and women a deficiency of the androgen hormones is at least partly to blame. These hormones are required to stimulate the production of water. 2. Sjögren’s syndrome. This is an ‘autoimmune’ condition in which the body’s immune system attacks the lacrimal gland so reducing water production. The cause is not known. It is much more common in females than males. Sjögren’s syndrome may involve other parts of the body, for example the mouth may also be dry. Other conditions, for example rheumatic disorders, may occur at the same time. 3. Other disorders, such as blepharitis may also cause ‘dry eye’ in the broad sense of this term (see above) by reducing the production of the other components of the tear film. For example in blepharitis it is the lipids that are deficient.

Diagnosis of dry eye

This is made from the symptoms and also the examination findings. I search for abnormalities which are characteristic of dry eye. These include roughness of the eye surface shown by staining with the red dye Rose Bengal and the presence of minute filaments attached to the eye. The Schirmer test uses a special strip of medical paper to measure tear production.

Dry eye

Dry eye stained with Rose Bengal red dye showing the dry rough areas

Treatment of dry eye

I will advise you on an individual basis which of the treatment options are appropriate for you -

Tear supplements are the mainstay of treatment and are available as artificial tears (e.g. hypromellose, Tears Naturale, Liquifilm Tears, Celluvisc, Hycosan) and more viscous gels (Geltears, Viscotears). These are available in preserved and un-preserved form the latter are more expensive. The artificial tears are quite thin and sometimes need to be used rather frequently, for example every hour or two. The gels are thicker so are used less frequently, for example four times daily, but may cause temporary blurring of vision especially if too much is applied. For many patients, occasional use of tear supplements is all that is required to reduce the symptoms of dry eye to an acceptable level.

Tear duct occlusion is the most effective treatment when tear supplements are insufficient. It works by retaining residual natural tear film or artificial tears on the eye for long periods. Generally I do reversible occlusion by inserting a tiny plastic plug into the opening of the tear duct. Insertion takes a few seconds and causes no pain. The plug is invisible to the naked eye and can easily be removed if necessary. Permanent occlusion of the tear ducts can be done for severe cases and is often highly effective.

Anti-inflammatory agents are necessary in some patients. These include steroid eye drops and Cyclosporin drops. These reduce the inflammation that is associated with both the age-related and Sjögren’s type of dry eye.

Agents that stimulate water production by the lacrimal gland are taken by mouth eg: Salagen. This also increases saliva production in cases of dry mouth.

The future

Many agents are under evaluation, for example Androgen hormone supplements. This is a logical treatment since age-related dry eye is caused partly by a deficiency of these substances.