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Glaucoma

Glaucoma is an eye diseases in which the optic nerve at the back of the eye is damaged. This eventually leads to vision loss because signals from the eye can’t reach the brain.

In most people it is due to an increase in eye pressure due to a problem with the drainage of fluid out of the eye. Anyone can get glaucoma however there are certain factors that can increase the risk.

 

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What is glaucoma?

How does the eye work?

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 The eye acts much like a camera. Light rays from an object enter the eye through the cornea, the clear front surface or “window” of the eye.

The cornea refracts or “bends” light rays so that they pass through the pupil of the eye. The light rays passing through the pupil are then focused by the lens of the eye onto the retina (which acts like the film of a camera).

These light rays are changed by the retina into electrical signals that are transmitted to the brain via the optic nerve, which is like a “cable” connecting the eye to the brain. The brain processes these signals into “pictures” that we see.

 

What is eye pressure?

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Like a football or tyre, the eyeball also needs pressure to maintain its shape. In the eye a water-like fluid called aqueous maintains the pressure.

This fluid is made in the back part of the eye in an area called the ciliary body. It then circulates inside the eye providing oxygen and nourishment to eye tissues. It then drains out the front part of the eye in an area called the drainage angle (or ‘drainage canal’) and into the bloodstream.

Normally this fluid is made at the same rate as it is drained and the eye pressure remains stable. The eye pressure for most people ranges between10 to 21 mmHg (millimetres of mercury). However, if there is a problem with the drainage of fluid then it builds up and the eye pressure rises

 

What is glaucoma?

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Glaucoma is the name given to a group of eye diseases in which the optic nerve at the back of the eye is damaged. This leads to vision loss because signals from the eye can’t reach the brain. In most people it is due to an increase in eye pressure because of a problem with the drainage of fluid out of the eye.


What are the symptoms of glaucoma?

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With the exception of acute glaucoma (see below) there are no symptoms of glaucoma until very late.

Glaucoma is often called the “sneak thief of sight” as you lose vision without realising it. This is because it affects the side vision first and then slowly works its way inwards to cause ‘tunnel vision’. Eventually the ‘straight ahead’ vision is also lost leading to blindness.

Sadly the damage done from glaucoma cannot be reversed so it is important to prevent vision loss from occurring in the first place. Thankfully with treatment vision can be saved for most people.

 

Who is at risk of glaucoma?

Anyone can get glaucoma however the following factors increase your risk:

  • Increasing age: although glaucoma can affect you at any age, it is much more common as you get older, particularly over 60 years.

  • Family history: If you have a parent, brother or sister with glaucoma you risk is increased.

  • Ethnicity: Glaucoma is common in Caucasians, Asians and Indians. It is less common in Polynesians and Maori.

  • Short-sightedness or long-sightedness

  • Previous eye injury

  • High blood pressure

  • Diabetes

  • Past or present use of steroid treatment

  • Migraines

 

When should you be checked for glaucoma?

The only way to detect glaucoma early is to have regular eye examinations. If you have risk factors for glaucoma your first eye check should be no later than the age of 40 years. If you don’t have risk factors then no later than the age of 45 years is recommended.

 

What are the different types of glaucoma?

Primary Open Angle Glaucoma (POAG)

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In New Zealand this is the most common type of glaucoma. This is a chronic (long-term) disease that occurs slowly. Although the drainage part of the eye is open it does not work well leading to a gradual build-up of fluid in the eye. This causes high eye pressure that damages the optic nerve. The exact cause of POAG remains unknown.

Normal Tension Glaucoma (NTG)

In this type of glaucoma the optic nerve is damaged even though the eye pressure is normal. People with NTG may have a very sensitive optic nerve or the blood supply to the nerve may be affected. This is also a chronic disease that occurs slowly.

Ocular Hypertension (OHT)

This is a condition where the eye pressure is high but there are no signs of glaucoma yet. Patients with OHT are at risk of developing glaucoma and sometimes need to be treated to lower the eye pressure back to normal.

Acute (angle closure) Glaucoma (ACG)

This occurs when fluid builds up behind the iris causing it to bulge forwards suddenly blocking the drainage part of the eye. This leads to a very rapid (hours) rise in eye pressure and is an emergency as damage to vision occurs in a very short time. An attack of acute glaucoma causes severe eye pain and redness, nausea and vomiting, blurred vision and/or halos around lights. Urgent laser treatment is needed to treat this condition (see below).

Secondary Glaucoma

This is when glaucoma develops as a result of another condition in the eye such as trauma, inflammation, or diabetes. Other types of glaucoma in this category include pseudoexfoliative glaucoma and pigmentary glaucoma.

People who have a narrow drainage angle because of the shape of their eye are at risk of this condition and need laser treatment to prevent ACG.

 

How do we diagnose glaucoma?

At Eye Surgery Associates you will have a comprehensive eye assessment in which the most advanced technology currently available is used to check for glaucoma. You can expect the following to be performed:

Eye and medical history

Eye exam including:

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  • Vision test

  • Slit-lamp microscope exam of the front of your eye

  • Measurement of your eye pressure

  • Measurement of corneal thickness (this can affect eye pressure)

  • A look at the drainage part of the eye using a special lens

  • Dilated pupil exam to look into the back of your eye at the optic nerve and retina



Visual field testing:

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this is a computerised test that maps out your entire field of vision to see if there are any missing patches. This is the best way to pick up the early loss of side vision that is seen with glaucoma.




Optical Coherence Tomography (OCT):

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this is a special optic nerve scan that can detect the earliest changes of glaucoma. This allows very early diagnosis as well as precise monitoring for glaucoma. At Eye Surgery Associates we use the Spectralis OCT provided by Heidelberg Engineering of Germany.





Stereo-disc photography:

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this provides a three-dimensional photograph of the optic nerve that is also used to help us monitor you for glaucoma.


How do we treat glaucoma?

Although there is no cure for glaucoma it can usually be controlled so that further loss of vision is prevented or at least slowed down. Treatment can save your remaining vision but does not improve eyesight.

At Eye Surgery Associates we provide a wide range of treatment options that have all been proven effective using clinical studies. There are medical, laser and surgical options available. The treatment that we decide upon will be individually tailored for each patient.

 

Medication for glaucoma

Eye drops:

There are several different eye drops that can be used to treat glaucoma. They work by lowering pressure in the eye to prevent worsening glaucoma. The drops need to be used regularly and often have to be used for life.

One or more of the following eye drops may be used:

  • Prostaglandin analogues (e.g. Hysite, Lumigan, Travatan)

  • Beta blockers (e.g. Timolol, Betoptic)

  • Alpha agonists (e.g. Alphagan)

  • Carbonic anhydrase inhibitors (e.g. Azopt, Trusopt)

  • Miotics (e.g. Pilocarpine)

  • Combination eye drops (e.g. Combigan, Cosopt, Duotrav)

Sometimes these eye drops cause side effects that can be troublesome and occasionally serious. You will be informed of possible side effects before any eye drop is started.

Tablets:

There is a medication called Diamox that can be used for glaucoma. Unfortunately it has several side effects that stop it from being used except in emergencies or special situations.

 

Laser treatment

Selective laser trabeculoplasty (SLT)

This is a laser procedure used for patients with open-angle glaucoma. The laser is applied to the drainage part of the eye to improve the flow of fluid out of the eye and hence lower eye pressure. It is often used when eye drops are not effective or cause troublesome side effects. It can also be used as an initial treatment for glaucoma in suitable patients.

SLT has an estimated success rate of 75% and typically lowers eye pressure by about 30%. The effect can last anywhere from 1 to 5 years and sometimes longer. SLT may need to be repeated if the effect wears off over time. Eye drops may still be needed for some people.

The procedure is performed in clinic and usually only takes a few minutes. The laser is painless and you can get back to your normal routine afterwards. The advantage of SLT is that it is very safe with no risk of vision loss or damage to the eye. Side effects are uncommon but are mild redness and temporary increase in eye pressure (5%).


Laser peripheral iridotomy (LPI)

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This is a laser procedure for patients with angle closure glaucoma or narrow drainage angles. The laser creates a tiny hole in the coloured part of the eye (the iris) which causes the iris to move backwards thereby unblocking the drainage part of the eye.

 

Glaucoma surgery

If medical or laser treatment does not relieve eye pressure then glaucoma surgery may be needed. At Eye Surgery Associates we provide the following surgical options:


iStent

The iStent is one of many newly developed procedures called ‘Minimally Invasive Glaucoma Surgeries’ or MIGS. The iStent is the worlds smallest medical device (length 1 mm). The iStent is recommended for patients with mild to moderate glaucoma and is usually performed with cataract surgery. It is therefore very useful for patients with both glaucoma and cataract. The tiny stent is placed into the drainage part of the eye to create a permanent opening for fluid to drain out of the eye and into the bloodstream.



Cataract Surgery

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Cataract surgery can help to treat closed angle glaucoma. By removing the cataract there is more space in the front part of the eye which leads to opening of the drainage angle. In some patients with open angle glaucoma removing the cataract can also lower eye pressure. At Eye Surgery Associates we have particular expertise in cataract surgery for glaucoma patients.





Trabeculectomy

This is the most common surgical procedure for glaucoma and allows the eye fluid to bypass the blocked drainage part of the eye. In this operation a small hole is made in the wall of the eye (the sclera). The hole is covered by a ‘trapdoor’ created from the outer part of the eye wall. Fluid from inside the eye drains through the small hole and out the sides of the trapdoor. The fluid drains into a small blister-like space under the outer lining of the eye (conjunctiva) before being absorbed by the surrounding eye tissues. The ‘blister’ is called a bleb and is located under the upper eyelid so it cannot be seen.






ExPRESS miniature glaucoma device

This is best considered a modified trabeculectomy operation. Instead of making a small hole a miniature stainless steel shunt (about the size of a grain of rice) is implanted under the ‘trapdoor’ created in the outer wall of the eye. Like trabeculectomy this allows the eye fluid to bypass the damaged drainage part of the eye to exit the eye more freely thus lowering eye pressure.







Glaucoma tube surgery

This operation is typically performed in patients are not suitable for one of the above procedures. A flexible plastic tube is inserted throught the eye wall into the front part of the eye to help drain fluid from the eye. At the other end of the tube is a small pouch that the fluid drains in to before being absorbed into surrounding tissues.








Cyclophotocoagulation

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This procedure is used for severe glaucoma when all other options have been unable to lower the eye pressure. A very strong laser in applied to the part of the eye where fluid is produced (the ciliary body). This helps to reduce the amount of fluid being made hence lowering the eye pressure. Sometimes the eye pressure can become too low after this procedure which is why it is not commonly used.

 
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