‘Dry eye’, known medically as keratoconjunctivitis sicca or keratitis sicca, is a condition where there is a problem with the production of tears.
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.
Why are tears important?
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.
What about the tears when I cry?
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.
What causes the problems with the tears?
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. This condition can also involve a type of arthritis.
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
This test finds out how long after blinking the eye starts to dry out.
The doctor uses eye-drops with a special dye in them. The doctor puts the drops into your eye, then will ask you to blink a number of times and then to stop and keep your eyes open without blinking. The doctor 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. The dry patches are shown up by the dye. 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. The dye does not change the colour of your eye and only stays in your eye for a short time.
Rose Bengal staining
This test uses another dye which stains damaged tissue. It allows the doctor to see any areas of the front of the eye where there may be problems.
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.
There are three main ways to help with dry eye:
- Preserving the existing tear flow
- Using artificial tears
- Reducing the draining away of the tears
Preserving the 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.
Using 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:
There are 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 pharmacy, 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.
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 put into your eyes as often.
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.
Is it possible to use too many 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.
Reducing the draining away of the tears
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 because the drainage holes are called punctata, and ‘occlusion’ is the medical term for closing up.
How is punctal occlusion done?
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.
Will these treatments and procedures cure my dry eye?
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.
Is there anything else that can help?
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.
Will dry eye affect my 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, any 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.