Dry eye syndrome can be caused or made worse by many things, including your environment, illnesses, side-effects of medicines, hormonal changes and simply getting older. In many cases there isn't one single, identifiable cause - it's often a mixture of things, as explained below.
We tend to take tears for granted, only noticing them if we laugh or cry. However, our eyes are always covered by a thin layer of liquid, known as a tear film. Tear production is regulated by the lacrimal functional unit, which is made up of the following parts:
- The lacrimal gland
Produces a liquid substance that makes up the majority of the tears
- The meibomian gland
Produces a fatty liquid that makes up the outer layer of the tear film, to hold the tear in place
- The eyelid
Spreads tears across the surface of your eye when you blink
- The cornea
A clear layer at the front of the eye, containing glands which contribute to the liquid that makes up tears
- The tear ducts
Two small channels at the inner/nasal side of the eye that allow tears to run off into the nose
If any part doesn't work properly, the whole system can break down, resulting in dry eye syndrome due to one or both of the following:
- The eyes cannot produce enough tears
- Tears evaporate before the body has a chance to replace them
In addition, when the eyes are no longer adequately protected by the tear film, the immune system tries to compensate by sending special, infection-fighting cells to the eye. It is these cells that cause the inflammation associated with more serious cases of dry eye syndrome. As you can see below, there are a number of environmental conditions that can affect tear production and function.
Environmental factors that can have a drying effect on the eye, causing tears to evaporate too quickly, include:
- Dry climate
- Central heating
- Warm blowing air
- High altitude
People tend to blink less often when carrying out activities that require visual concentration, such as reading, writing or working with a computer. This can cause tears to evaporate faster than usual, leading to dry eyes.
Several types of medicine are thought to cause dry eye syndrome in some people. These include:
- Oral contraceptive treatment
*Often used to treat high blood pressure (hypertension)
Some people experience dry eye syndrome after laser-assisted in-situ keratomileusis (LASIK) surgery, a procedure used to correct eyesight problems. However, these dry eye symptoms usually clear up after a few months.
Contact lenses can irritate the eye and cause dry eye syndrome in some people, but changing to a different type of lens - or limiting their use - will usually help to resolve the symptoms.
The hormonal changes that occur during the menopause can lead to a reduction in tear production, resulting in dry eye syndrome.
Most people with dry eye syndrome also have blepharitis, which is inflammation of the rims of the eyelids. Blepharitis is commonly associated with:
- Seborrhoeic dermatitis
Other medical conditions that can cause dry eye syndrome in some people include:
- Contact eczema
- Sjögren's syndrome
- Rheumatoid arthritis
- Previous trauma such as burns or exposure to radiation
- Bell's palsy
We naturally produce fewer tears as we get older. This, combined with the effects of the menopause, probably explains why dry eye syndrome is particularly common among older women.