About dry eye
Dry eye known medically as keratoconjunctivitis sicca or keratitis sicca, is a condition where there is a problem with the production of tears.
How the eye works
We need light to see what is around us and to see colour. Light bounces off the objects we look at. These reflect different amounts of light which we see as different colours.
Front of the eye
Light rays enter the front of our eye through the clear cornea and lens. It is very important that both the cornea and lens are clear as this allows the light to pass directly through the front of the eye to the retina.
The cornea and lens bend light so that it can focus on the retina at the back of our eye. This gives us a clear, precise image. The cornea focuses the light towards our retina. The lens fine tunes the focussing of this light.
Our tears form a protective layer at the front of the eye and also help to direct the light coming into our eye.
The iris, the coloured circle at the front of our eye, changes the size of the pupil which allows different amounts of light into our eye.
The pupil is the dark hole in the middle of the coloured part of our eye. The pupil gets smaller in bright conditions to let less light in. The pupil gets bigger in dark conditions to let more light in.
Middle of the eye
The middle of our eye is filled with a jelly-like substance called the vitreous. The vitreous is clear and allows light to pass directly from the front to the back of our eye.
Back of the eye
The retina at the back of the eye is a light-sensitive layer which consists of rod and cone cells. These cells collect the light signals directed onto them and send them as electrical signals to the optic nerve at the back of our eye.
Rod cells are concentrated around the edge of the retina. They help us to see things that aren't directly in front of us, giving us a rough idea of what is around us. They help us with our mobility and getting around by stopping us from bumping into things. They also enable us to see things in dim light and to see movement.
Cone cells are concentrated in the centre of our retina where the light is focused by the cornea and lens. This area is called the macula. Cone cells give us our detailed vision which we use when reading, watching TV, sewing and looking at people's faces. They are also responsible for most of our colour vision.
The optic nerve is made up of thousands of nerve fibres. These fibres pass the electrical signals along to our brain where they are processed into the image we are looking at.
How we see
Seeing can be likened to the process of taking pictures on a film with a camera which you then get developed. The retina is like a camera film which stores an image of what we are looking at. The image directed onto the retina is then sent along to the brain where it is processed, like developing a camera film. Therefore we actually 'see' in our brain with the light information sent to it from our eyes. This whole process happens very quickly so that everything we see is in focus.
Symptoms of dry eye
Usually eyes feel irritated, scratchy, dry and uncomfortable. Eyes may be red and there may be a burning sensation, or it may feel as if there is something in the eye like grit or an eyelash. Sometimes there may be periods of blurred vision but these normally go away after a short while or on blinking. Sometimes eyes may water too much and often eyes won't actually feel dry but you may notice that there are no tears when you are upset or when peeling onions.
How tears are produced
Tears are important as they form a layer on the very front of the eye. Called the tear film, this layer does a number of things. The tear film takes a part in the focusing of light into the eye but it mainly lubricates the eye keeping it moist and smooth. The tear film is actually made up of three layers each with a different function.
The layer closest to the eye is called the mucin layer. It coats the cornea which is the clear window at the front of the eye; it forms a foundation for the other layers of the tear film.
The middle layer is called the aqueous layer. This is the watery layer that most people think of when they think of tears. This layer is produced by the lacrimal gland which is underneath the upper eyelid. This layer provides moisture and supplies oxygen and other important nutrients to the cornea. This layer is mainly water.
The outer layer is called the lipid layer. This is an oily film which seals the tear film to the eye and helps to prevent any evaporation.
Evaporation is the technical name for the watery layer being lost into the air.
The mucin and lipid layers are produced by small glands around the eye. Each time we blink the tears are spread onto the front of the eye.
Excess tears are drained away by tiny drainage holes on the inside of the eyelids, these holes channel the excess tears into the nose. This is why crying sometimes makes your nose run.
Tears caused by peeling onions
As well as being produced all the time to keep the eye moist, tears are also produced by a reflex - a reflex is the body's automatic response to certain situations. Emotion, peeling onions or an injury, for example poking your eye, will produce excess tears. However these tears drain away quickly and do little to soothe a dry eye.
Causes of dry eye
Dry eye has a number of causes. It happens mostly as a part of the natural ageing process but can also be caused by problems with blinking or problems with the glands which produce the tears. Some drugs can cause dry eye, like antihistamines and oral contraceptives. Contact lenses carry an increased risk if you have dry eye.
Sometimes dry eye is also a symptom of other conditions affecting other parts of the body particularly arthritis or a condition called Sjogrens syndrome. Sjogrens syndrome is a condition where, as well as dry eyes, people can also have a dry mouth and a dry vagina. This condition can also involve a type of arthritis.
Diagnosing dry eye
Firstly there are a number of tests which the doctor may want to do to work out how dry your eyes are. These tests can give them an idea on how to treat you. The tests check how many tears you produce and detect any areas on the front of your eye that doesn't have enough tears.
There are three main tests:
Tear film break-up time
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This test finds out how long after blinking the eye starts to dry out.
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The doctor uses eye-drops with a special dye in them.
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The doctor instils the drops (puts the drops into your eye), will then ask you to blink a number of times, and then to stop and keep your eyes open without blinking.
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The doctor then uses a coloured light so that they can see the dye and time the period between your last blink and the formation of dry patches.
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The dry patches are shown up by the dye.
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If your eyes start to show these patches of dryness before ten seconds then it usually means that there is some evidence of a dry eye.
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The dye does not change the colour of your eye and only stays in your eye for a short while.
Rose Bengal staining
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This test uses another dye.
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The dye stains damaged tissue.
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It allows the doctor to see any areas of the front of the eye where there may be problems.
Schirmer test
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This is a test with filter paper which may be performed to test tears. It is not performed as often as it used to be.
Treatment
There are three main ways to help with dry eye:
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Preserving the existing tear flow
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Using artificial tears
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Reducing the draining away of the tears.
Preserving your existing tears
There are certain things that you can do yourself which may help reduce the symptoms of dry eye.
You can lower the temperature in rooms, since high temperatures make the tears evaporate more quickly. Central heating can make the air quite dry and sitting directly in front of a heating source like the fire can also be a problem. Obviously this needs to be balanced with the need for keeping warm especially for older people. Sometimes humidifiers can help by moistening the air.
Many people find that dry eye is worse during tasks such as reading or computer work. This is usually because we unconsciously blink less when we are doing anything that needs lots of visual attention. It may help you to make an effort to blink more when doing these tasks.
Artificial tears
Artificial tears in the form of eye drops are usually the mainstay of treatment for people with dry eye. The aim of the treatment is to supplement the tears and therefore make the eye more comfortable. They also stop any damage to the front of the eye from prolonged dryness.
There are three main types of tear substitutes that you may be prescribed:
Drops
There are very many brands of artificial tears. Although the reasons are not yet clear, some brands suit some people better than others.
Often the doctor will suggest a selection of different brands of drops for someone to try. Usually asking for one drop to be used for a month at a time to see which one gives the best result. The doctor may suggest that you keep a note of how your eyes are day to day, this is sometimes called a symptom diary, so that you can look back and check how each of the drops worked.
Most drops are available over the counter at the pharmacist, they are also usually cheaper than a prescription charge. Unless you are entitled to free prescriptions, it may be worth you just buying the drops over the counter, as this can work out cheaper than multiple prescription charges.
The main problem with drops is that they are only effective for a short period and need to be used very frequently. Some people also develop sensitivity to the preservative used in the drops, but preservative-free drops are available if this should happen.
Gels
There are a number of products which are similar to drops but which are made from a different chemical. These gels last for longer and so are sometimes more useful. They do the same thing as the ordinary drops but usually don't have to be instilled (put into your eyes) as often.
Ointments
Often you may be prescribed with an eye ointment to help preserve the tears and moisten your eye. These are particularly useful to use overnight. They are used overnight because they are quite sticky and would interfere with vision during the day, but this doesn't matter as you sleep. They can be useful because, as you sleep, sometimes the eyes aren't fully closed. This means the tears have a chance to evaporate.
When you wake your eyes can then be very dry. Ointments stop this happening, so much so that your eyes are more comfortable in the morning.
Using eye drops
Artificial tears are only meant to help lubricate the eye, which means that they can be used very regularly. Your doctor may suggest that you start using the eye drops once every hour, and then less frequently as you start to gauge how well you are responding to them. There is no problem using the eye drops this frequently all the time, but using them very regularly may mean that you become sensitive to the preservative in the drops more quickly than you would otherwise. If it feels necessary to use your drops very frequently then your doctor may well want to review your treatment and prescribe preservative free drops or possibly look at other ways of helping you.
Preventing tears draining away
It is possible to help dry eye by stopping the draining away of the tears. This is done by blocking up the two drainage holes in the lower eyelids. This process is called punctal occlusion. 'Punctal' because the drainage holes are called punctata, and 'occlusion' is the medical term for closing up.
About punctal occlusion
Usually it is tried on a temporary basis first to see if permanent occlusion will be of benefit. The small drainage channels are blocked by little plugs called punctal plugs. This stops the tears draining away and hopefully helps to relieve the symptoms of dry eye by keeping the tears in the eye for longer. It is done temporarily at first with a dissolving plug to ensure that the permanent occlusion will not cause the eyes to water unnecessarily, the medical term for which is epiphora.
Permanent closing of the drainage holes is normally done with plugs that don't dissolve. However if there are any problems once these plugs are inserted they can still be removed.
Treatment effectiveness
Unfortunately these treatments cannot 'cure' dry eye for good. They can however significantly reduce the symptoms of dry eye meaning that the symptoms will be less of a problem for you.
Other ways to help dry eye conditions
There has been a lot of debate about the role of diet in dry eye. Some people say that fresh fruit and certain oils - omega 3 and 6 - can be of benefit. However there are no large-scale scientific studies which prove this.
Effect of dry eye on eye sight
Dry eye on its own should have no effect on your vision, it does not cause permanent sight loss. There may be some temporary blurring of vision but this is normally relieved by blinking. It can make the eyes very sore so reading or any close work might be uncomfortable.
The main aim of all the treatments is to stop both the symptoms and any damage which might occur to the front of the eye. Although rare, damage to the front of the eye may threaten some sight. The treatment stops this damage and it is normally effective in the long term, meaning that your sight will not be affected in any way.
What next?
Talk to someone
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Whether you want to know more about your eye condition, buy a product from our shop, join our library, find out about possible benefit entitlements, be put in touch with a trained counsellor, or make a general enquiry, we're only a call away.
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Telephone: 0303 123 9999
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We are ready to answer your call Monday to Friday 8.45am to 6.00pm and Saturday 9.00am to 4.00pm. Outside these times leave us a message and we'll get back to you as soon as possible.
Unfortunately, RNIB can only answer email enquiries from the UK. But you may find an organisation for people with poor sight in your country through our organisations database.
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RNIB's guide to Adapting to sight loss offers ideas for people with sight problems on making life easier and ways of getting the most out of life.
You may also find the following useful:
Useful contacts
At the moment RNIB is not aware of an organisation which specialise in Dry Eye.
There is a Sjogrens Syndrome Society in the UK and you may wish to contact them. They can be reached at
British Sjögren's Syndrome Association (BSSA)
PO Box 10867
Birmingham
B16 0ZW
Tel: 0121 455 6532
About this guide
Copyright © RNIB September 2008
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