DRY EYE
by Royal National Institute for the Blind
What is it
Tears serve to lubricate the eye and they are produced around the clock, but
when insufficient moisture is produced stinging, burning, scratchiness and
other symptoms are experienced and may be referred to as Dry Eye, Keratitis
Sicca, Keratoconjunctivitis Sicca (KCS) or Xerophthalmia.
When we blink, tears form a film which spreads over the eye, making the
surface smooth and optically clear and enabling good vision.
There are three layers in the thin film of tears: an oily layer, a watery
layer and a layer of mucus, each with specific function.
The outermost, oily layer is produced by small glands at the edge of the
eyelid (meibomian glands) and the main purpose of this layer is to smooth the
tear surface and reduce evaporation.
The middle, watery layer, is produced by small glands scattered through the
conjunctiva, (the delicate membrane lining the inside of the eyelid) and by the
large lacrimal (tear) gland. This layer cleanses the eye and washes away
foreign particles or irritants.
The innermost layer consists of mucus which allows the water layer to spread
evenly over the surface of the eye. Without mucus, tears would not adhere to
the eye.
What causes it
Dry eye is caused when the tear gland produces insufficient tears. This can
happen as part of the normal ageing process, and is more common among women so
although the condition is not common it tends to occur with increasing age when
it is not always noticed because the effect of dry eye tends to balance another
age-related change; poor tear drainage. The result of this is a balance between
not making too much lacrimal fluid (tears) and not being able to drain away
much lacrimal fluid.
The main causes of an insufficient film of tears are deterioration of
lacrimal tissue, dysfunction of the Meibomian gland destabilizing the film of
tears or a blockage in the excretory ducts of the lacrimal gland.
People with Sjogren's syndrome are at risk of dry eye as part of a more
systemic problem involving salivary glands and other sites of mucous membrane.
Salivary gland involvement produces a dry mouth as well. This syndrome, and dry
eyes generally, may be found in people with rheumatoid arthritis.
Effects of the condition
In the early stages there is an increase in mucus strands and as the tear
film breaks down, the mucin layer becomes contaminated. Where this contaminated
matter cannot be dispersed it tends to move with blinking. Mucin is a substance
which dries very quickly and rehydrates very slowly. People with dry eye rarely
have a sensation that the eye is dry but instead experience irritation,
burning, a sensation of having a foreign body in the eye, mucus discharge and
possible temporary blurring of vision.
Blinking may cause pain to people with severe forms of keratitis.
Treatment
There is a series of tests designed to identify the cause and type of dry
eye and these include Rose bengal staining where a dye is used to identify
problems and Schirmer's test which involves measuring the amount of wetting of
a special filter paper. This can be done with or without topical anaesthetic
which may be in the form of eye drops.
The aim of treatment will be to relieve discomfort and prevent corneal
damage.
In some situations relief may be found by blinking consciously when doing
close or continuous work. It is also helpful to close the eyes for a spell from
time to time.
Eye drops may be prescribed or purchased over the counter and since there is
a variety, it may be helpful to try others if your present product does not
suit you.
Some drops contain preservative which means they are safe to use for a month
after opening, but although these drops are cheap and suitable for most
sufferers, some people do not tolerate the preservative and may need to get
prescription from the hospital pharmacy for a preservative free medication.
Lubricant ointments are also helpful, particularly at night. These are also
available without preservative.
Some women benefit from hormone replacement therapy (HRT), especially those
whose dry eye problems began around or after the menopause.
Antihistamines or certain types of travel sickness pills, inhibit tear
secretion and symptoms can vary from day to day and be affected by general
health.
Surgical procedures may be indicated if symptoms are severe despite drops.
It involves closing the tear drainage holes in the eyelids permanently. It is a
minor operation which is suitable for some patients.
Helping People with Dry Eye
Avoiding the following situations will minimise your risk of Dry Eye.
- reduce the dry atmosphere caused by central heating by using a humidifier
- avoid car heaters, particularly at face level
- sit away from direct heat such as gas or electric fires
- use eyedrops just before activities which cause additional pain or
discomfort such as television, reading, sewing and writing
- remember to blink regularly, particularly when doing close or concentrated
work. Blink properly with full lid closure, not "half" blinking.
- avoid smoky atmospheres.
Prognosis
Prognosis varies considerably and may depend in part upon individual
lifestyle choices and overall health as well as the severity and cause of the
condition. There is no definite cure, but people can usually be made more
comfortable.
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