What causes acute glaucoma?
To understand the cause, it helps to understand how
fluids work in the eye. The eye needs to keep its shape so that light
rays are focussed accurately onto the retina. So, most of the eye is
filled with a substance like jelly called the 'vitreous humour' (humour
meaning fluid). The front of the eye is filled with a clear fluid
called 'aqueous humour', which is more watery.
The aqueous
humour is made continuously by cells called the 'ciliary body'. The
fluid circulates through the front part of the eye, and then drains
away through an area called the 'trabecular meshwork', which is located
near the base of the iris. So, there is constant production and
drainage of fluid.
What happens in acute angle glaucoma?
In
acute glaucoma, there is a sudden blockage, so that aqueous fluid
cannot drain out of the eye. This happens if the iris (the coloured
part of the eye) gets too close to the lens. Fluid gets stuck behind
the iris and makes it bulge forwards. This bulging then blocks the
drainage area (the trabecular meshwork), so that fluid cannot leave the
eye. But more fluid is still being made, so the pressure inside the eye
starts to rise quickly.
What causes the blockage?
Usually it is a
combination of factors. In some people, the area near the base of the
iris is very narrow, so it more easily gets blocked. In other people,
the lens of the eye may be swollen, which has the same effect. This
situation is called a 'narrow drainage angle' or 'shallow anterior
chamber' and makes a person more susceptible to acute glaucoma.
The
iris (the coloured part of the eye) is also involved. The iris muscle
is responsible for controlling the size of the pupil (the black area in
the middle of the eye). When the iris muscles enlarge the pupil, they
tend to bulge, which can block the flow of fluid if the area is already
narrow. The pupil enlarges in conditions of dim light, sudden
excitement, or with certain medications. For this reason, acute
glaucoma is more likely to occur in the evening, or in situations like
watching a football match on TV (dim lighting and sudden excitement).
What can trigger acute glaucoma?
Various
medications can trigger acute glaucoma if you are susceptible to it.
However, for the population as a whole, the chance of getting acute
glaucoma with these medicines is very small - so they are commonly
prescribed without too much worry. But if you have been warned that you
may be susceptible to acute glaucoma, tell your doctor before starting
new medication or eye drops, especially if it is one of the ones listed
below.
Commonly used medicines which may trigger acute glaucoma are:
- Eye drops used to dilate (enlarge) the pupil - they may be used for eye checkups.
- Antidepressants of the 'tricyclic' or 'SSRI' types.
- Some of the medicines used to treat nausea, vomiting or schizophrenia (a type called 'phenothiazines').
- Ipratropium (used for asthma).
- Topiramate.
- Some medicines used to treat allergies or stomach ulcers, such as chlorpheniramine, cimetidine and ranitidine.
- Medication used during a general anaesthetic.
Lying on your front (for a long period) may also affect fluids
in the eye, and can trigger acute glaucoma. This can occur, for
example, during an operation on the spine.
Who gets acute glaucoma?
Approximately 1 in
1000 people get acute glaucoma. It is more likely in people over age 40
years, and most often happens at around age 60-70 years. It is more
common in long-sighted people and women. It is also more common in
certain populations: Southeast Asian and Eskimo people.
What are the symptoms of acute glaucoma?
The symptoms usually start suddenly. They are:
- Sudden, severe pain in the eye.
- Redness of the eye.
- Reduced vision, often with 'haloes' (circles) seen around lights.
- The pain may be spread around the head and be felt as a severe headache.
- Sometimes, the pain may cause nausea, vomiting, or there may be abdominal pain (tummy pain) as well.
- Some people may not get eye pain, but instead have some of the
other symptoms listed here, such as headache or abdominal pain with a
red eye or reduced vision.
- The pupil (black part of the eye) will look large, and the clear part of the eye looks hazy ('milky' or 'steamy').
As explained above, symptoms often begin in a situation of dim
lighting, sudden excitement, with certain medications or after a
general anaesthetic.
Are there any warning symptoms?
Acute
glaucoma can start 'out of the blue' with no warning. However, you may
have warning symptoms, which often are not recognised. These occur when
pressure rises in the eye, and then improves by itself. The symptoms
are: blurred vision, seeing haloes or rainbows around lights, and eye
pain. The warning symptoms can come and go - they may start in the
evening (with dim light), and may settle after sleep (because sleep
relaxes the iris muscles).
If you have these symptoms you should see a doctor urgently, in case you need treatment to prevent a more severe attack.
How is acute glaucoma diagnosed?
The
diagnosis is made from the symptoms and the appearance of the eye. A
provisional diagnosis can be made by any doctor (not necessarily an eye
specialist). The diagnosis can be confirmed by an examination done by
an eye specialist. This usually involves measuring the pressure in the
eye (a quick and easy test) and examining the eye using a special light
and magnifier called a 'slit lamp'.
What is the treatment for acute glaucoma?
Initial treatment
Treatment is very urgent.
You should be seen by an ophthalmologist (eye specialist) immediately.
If it will take time getting to the ophthalmologist, treatment can be
started meanwhile.
The first treatment is medication to lower
the pressure of fluid in the eye. There are various types of medicine
that reduce eye pressure. Different combinations can be used, depending
on your medical history. The usual treatment is:
- An intravenous injection of acetazolamide.
- Eye drops containing beta-blocker medication (to reduce fluid in the eye) and steroid (to reduce inflammation).
Other treatments which may be used initially are:
- Painkillers and anti-sickness medication, if needed.
- Usually, it is recommended that you lie flat on your back - this position may help drain the trapped fluid.
- Other types of eye drops which reduce fluid in the eye, such as brinzolamide, brimonidine or pilocarpine.
- Other fluid-reducing medication such as intravenous mannitol.
Further treatment
When the pressure in the
eye has gone down, further treatment is needed in order to prevent the
acute glaucoma from coming back. This involves using laser treatment or
surgery to make a small hole in the iris. The hole allows fluid to flow
freely around the iris, which stops the iris bulging forwards and
blocking the trabecular meshwork.
Laser treatment is called
'peripheral iridotomy'. This is the usual treatment, and the preferred
option, as it does not involve surgery to the eye. Two small holes are
made in the iris using a laser. The holes are almost unnoticeable to
other people.
Surgical treatment is called surgical iridectomy.
It makes a small, triangular hole in the iris. The hole is visible
afterwards as a very small, black triangle at the edge of the iris.
Sometimes,
another type of surgery is used, which is similar to a cataract
operation. This operation removes the lens of the eye - which can help
if a swollen lens was causing the acute glaucoma in the first place. As
with cataract operations, the lens which is removed can be replaced by
an artificial lens, or by using glasses.
Usually, laser or
surgical treatment will be advised for the other eye at some stage.
This is to prevent acute glaucoma happening in the other eye. Also, eye
drops may sometimes be needed as long-term treatment, to help keep the
eye pressure under control.
What are the complications of acute glaucoma?
If
treatment is delayed, the high pressure in the eye can damage nerves
and blood vessels. This can cause reduced vision, and in severe cases
can cause blindness in the affected eye.
Also, delayed treatment
can lead to the the iris (thecoloured part of the eye) sticking to the
front of the eye (cornea). This blocks the drainage area, so a
'drainage operation' is needed. This operation creates a channel
between the inside of the eye and the outside (white part) of the eye.
What is the outlook for acute glaucoma?
The
outlook is good if treatment is given promptly. The eye can recover,
and laser treatment or surgery can prevent the problem coming back.
If the attack is severe or if treatment is delayed, there is a risk of complications (explained above).
Driving and glaucoma
Many people will be
allowed to drive after recovering from acute glaucoma. Even if vision
is reduced in one eye, you may still be allowed to drive if your vision
is good enough in the other eye. However, you will need advice from
your eye specialist. If you are a driver and have glaucoma in both
eyes, the law says that you must inform the Driver and Vehicle
Licensing Authority (DVLA).
How can acute glaucoma be prevented?
Some
people have an increased risk of getting acute glaucoma, due to a
narrowing of the area where fluid normally drains from the eye. This is
called a 'shallow anterior chamber' or 'narrow drainage angle'.
Sometimes a narrow drainage angle is noticed at a routine eye
examination. You may be told about this and advised to be careful with
certain medications and eye drops (as above).
If you are at very
high risk of acute glaucoma, you may be advised to have treatment such
as laser iridotomy (above) to prevent it.
Be aware of the
symptoms of acute glaucoma. Anyone who has a red eye with pain or
vomiting, or a red eye with reduced vision, should get medical advice
immediately. If you take a new medication or have eye drops to dilate
the pupil, and then have symptoms of acute glaucoma, get medical advice
straightaway; tell the doctor about the medication and symptoms. This
makes it easier for the problem to be recognised early.
Disclaimer: This article is for information only and should not
be used for the diagnosis or treatment of medical conditions. EMIS and
PiP have used all reasonable care in compiling the information but make
no warranty as to its accuracy. Consult a doctor or other health care
professional for diagnosis and treatment of medical conditions.
© EMIS and PiP 2008 Reviewed: 25 Jul 2008
