Glaucoma


What is Glaucoma?

Glaucoma is the name given to a group of eye diseases, all of which have in common damage to the optic nerve in the back of the eye. Elevated pressure inside the eye is the most frequent risk factor for glaucoma development, although a small percentage of eyes will develop glaucoma with normal eye pressure. The optic nerve connects the eye to the brain and enables sight. If left untreated, glaucoma causes thinning of the optic nerve and a gradual reduction in vision starting with the peripheral vision. Over time this progresses to affect more and more of the vision constricting the vision to cause "tunnel vision". Later, it can lead to blindness. When detected early, treatment will prevent or reduce the loss of vision in most patients.

 

Vision loss due to Glaucoma is permanent, therefore it is important to have regular eye exams that include measurements of your eye pressure to detect it early on. Glaucoma is one of the leading causes of blindness .


What Causes Glaucoma?

Glaucoma is most commonly caused by high eye pressure. This is the result of inadequate drainage of the aqueous humour (a fluid inside the eye).  Aqueous humour is constantly circulating within the eye so the eye pressure can change throughout the day. Persistently high eye pressure can damage the delicate fibres of the optic nerve and cause glaucoma. However it is possible to have high eye pressure which is yet to cause any optic nerve damage. This is referred to as Ocular Hypertension, which is different to glaucoma.


Glaucoma can also occur in the setting of normal or low eye pressure. Decreased blood flow to the optic nerve caused by poor circulation in the blood vessels that nourish the optic nerve can cause optic nerve damage, sometimes referred to as Normal Tension Glaucoma.


Symptoms of Glaucoma

Glaucoma usually gives few warning signs. Infrequently, acute glaucoma attacks occur, and cause pain due to extremely high eye pressure from complete blockage of the aqueous fluid drainage.


Generally, there are no symptoms from glaucoma. It is impossible for a patient to notice it on their own, which is why all eye care professionals check for it during any Eye Examination.


Who is at Risk of Glaucoma? 

Glaucomas can occur at any age but are more common in middle-aged people. Some people have a higher than normal risk of getting Glaucoma. This includes people who:

  • Age 40 or over
  • Have a family history of Ocular Hypertension or have high eye pressure
  • People who are short-sighted (myopic)
  • Are of African or Hispanic heritage
  • People who are farsighted (Hyperopia)
  • Have corneas that are thin in the centre
  • Have diabetes, migraines, poor blood circulation
  • Have had an eye injury
  • Long-term steroid medication use
  • Pigment dispersion syndrome sufferers 
  • Pseudoexfoliation syndrome sufferers


How Does Ocular Hypertension Occur?

Ocular Hypertension occurs when the pressure in the eye (known as intraocular pressure) is above the range considered normal (above 21 mm Hg). 


It is distinguished from Glaucoma, a more serious eye condition, in that there are no detectable changes in vision, no evidence of visual field loss and no damage to the optic nerve.


What are the Types of Glaucoma?

There are many forms of glaucoma including:

  • Primary open-angle glaucoma
  • Angle Closure Glaucoma
  • Inflammatory Glaucoma
  • Lens-related Glaucoma
  • Traumatic Glaucoma
  • Iridocorneal Endothelial Syndrome (ICE)
  • Iridocorneal dysgenesis
  • Pigmentary Glaucoma
  • Pseudoexfoliative Glaucoma
  • Neovascular Glaucoma
  • Congenital glaucoma


Primary Open-Angle Glaucoma

Primary Open-angle Glaucoma is the most common type of Glaucoma

  • The angle between the iris and cornea is wide and open,
  • There is no other cause for the glaucoma
  • Usually has no warning signs. 


This is the most common form of glaucoma and usually develops slowly over many years. It often runs in families. There is no pain associated with this condition and, as it develops slowly, most people are unaware of its presence. This is the reason regular eye examinations are so important, particularly if you have a family history of glaucoma, as well as for everyone over 50 years of age.

 

Angle Closure Glaucoma

Angle Closure Glaucoma is a less common form of Glaucoma. 

  • The angle between the iris and the cornea is narrow or closed.
  • It occurs when a portion of or the entire drainage angle becomes anatomically closed so that the aqueous fluid within the eye cannot reach the trabecular meshwork. This inability to drain can cause a sudden buildup of pressure in the eye. (See acute angle closure glaucoma below)


Acute Angle-Closure Glaucoma

Acute Angle-Closure Glaucoma is an eye emergency, which requires immediate medical attention and treatment. Permanent damage to the optic nerve can result within hours of onset due to the high levels of eye pressure involved.


Patients may complain of the following symptoms: 

  • A severe headache,
  • Eye pain,
  • Nausea and vomiting,
  • Blurred vision,
  • Halos around lights, and
  • Eye redness.


Treatment of acute angle-closure glaucoma involves the use of intensive pressure-lowering eye drops, tablets, and laser to the iris to bypass the blockage in the eye. If these measures are unsuccessful, emergency surgery may be needed. Examination of the eye prior to an attack of angle-closure glaucoma may reveal the future likelihood of such an event and a prophylactic laser treatment (iridotomy) can be performed to prevent an attack.


Normal Tension (pressure) Glaucoma 

Normal Tension Glaucoma or low tension Glaucoma is a type of Glaucoma where the optic nerve is damaged despite normal intraocular pressure, due to poor circulation to the optic nerve.


Other types of glaucoma:

Congenital glaucoma is seen in babies and often runs in families. It is caused by improper development of the eye’s drainage canals before birth.


Uveitic glaucoma occurs in eyes that experience prolonged inflammation.


Pigmentary glaucoma occurs in eyes where the pigment on the back of the iris is rubbed off over time as the iris dilates and constricts on top of the natural lens of the eye. This pigment then blocks fluid from draining out of the eye through the trabecular meshwork, leading to high eye pressure.


Neovascular glaucoma occurs when abnormal blood vessels grow inside the front of the eye in response to vascular diseases in the back of the eye such as retinal vein occlusions and diabetes. The abnormal blood vessels block the trabecular meshwork leading to very high eye pressure. Neovascular glaucoma can be very challenging to treat.


Pseudoexfoliation glaucoma (often abbreviated to PXF or PEX glaucoma) occurs when a dandruff-like material is produced in the front of the eye. The material blocks fluid drainage through the trabecular meshwork. This type of glaucoma has a strong genetic component.


Glaucoma Diagnosis 

If Glaucoma is diagnosed early, vision loss can be slowed or prevented. If you have been diagnosed with the condition, you will generally need treatment for the rest of your life.


A regular Eye Examination is a key step in detecting Glaucoma early enough to successfully slow or prevent vision loss. 


As mentioned, people with any risk factors of Glaucoma should have an ophthalmologist perform a comprehensive Eye Examination that includes:

  • eye pressure measurement by placing a Tonometer on the cornea surface to measure how your eye resists slight pressure
  • gonioscopy (a lens with mirrors used in assessing the anterior chamber drainage pathway), 
  • dilating the pupils for an examination of the back of the eye
  • Pachymetry to measure corneal thickness
  • OCT (Optical Coherence Tomography) imaging of the optic nerve head and macula
  • Visual field test performed on an automated machine - the Humphrey Visual Field Analyser


Sometimes, patients may be identified as potential Glaucoma sufferers through a routine Eye Examination with an ophthalmologist. 

In some cases, the diagnosis is straightforward. In other cases, particularly early in the course of the disease, the diagnosis may not be certain; a review at a later time may be needed to definitively diagnose or exclude glaucoma.


It is important to maintain regular follow up with your ophthalmologist once a diagnosis of Glaucoma is made. 


Glaucoma Treatments

Glaucoma treatment is aimed at lowering the eye pressure to prevent further glaucomatous damage to the optic nerve. Glaucoma treatment can stabilise the disease but not cure it, meaning treatment is usually life-long.


Lowering the eye pressure can be achieved by different methods including:

  • eyedrops
  • laser treatment (SLT)
  • insertion of stents (and other minimally invasive glaucoma surgical techniques)
  • glaucoma filtration surgery


At this stage unfortunately no glaucoma treatment has been proven to repair the damage already done to the optic nerve or to improve any vision that has already been lost.


Eye Drops

At the early stage of the disease, patients can usually be managed medically with eye drops that lower the eye pressure. 


It is important to consult an ophthalmologist regarding the eye drops as some of them have significant side effects. 


Selective Laser Trabeculoplasty

Selective Laser Trabeculoplasty (SLT) uses short pulses of low energy light, aimed at the drainage angle at the front of the eye, to improve the outflow of fluid from within the eye – lowering eye pressure.


It is often used in Open Angle Glaucoma as a first line treatment (to negate the need for eye drops), as a supplement to existing medications (if the glaucoma damage is worsening) or if side effects from eye drops have become intolerable. 


The aim of SLT is to lower pressure within the eye. It does not improve vision. It is a safe and effective procedure with a very low complication rates.


Minimally Invasive Glaucoma Surgery or MIGS

If first line treatment for glaucoma (eye drops or laser) is unsuccessful in stabilising a patient’s glaucoma, or have proven unsuitable due to side effects, then surgery may be required.


Recently, new surgical treatments have been introduced called Minimally Invasive Glaucoma Surgery or MIGS. These surgeries, in comparison to traditional surgical techniques, have a lower complication rate and are often performed at the same time as cataract surgery. They can also be performed as a standalone procedure, and still allow for subsequent, traditional glaucoma drainage surgery if required.


There are a number of different MIGS procedures, but most commonly in Australia, this procedure involves the insertion of micro stents into the drainage angle of the eye, improving the drainage of fluid out of the eye.


These procedures have been shown to reduce eye pressure and are very safe.


Trabeculectomy or Tube Shunt

These operations are performed at day surgery under local or general anaesthetic.


Trabeculectomy: An alternative drainage pathway for fluid within the eye is created by making a small opening in the wall of the eyeball (sclera) and into the front chamber of the eye. Fluid then drains from within the eye, out through the hole, and into the vessels of the membrane covering the eye (conjunctiva). The flow of fluid into the space underneath the conjunctiva causes a raised blister or ‘bleb’ that helps control the flow of fluid out of the eye – allowing a lowering of pressure without it becoming too low. The drainage bleb typically sits, hidden, underneath the upper eyelid.


This procedure typically takes 1 to 2 hours to perform, under local or general anaesthesia, and has been used to treat advanced Glaucoma for over 40 years. Although the complication rates are relatively higher than MIGS surgeries, the pressure lowering effect is typically greater, and lasts longer.


Tube Shunt: This procedure is similar to a trabeculectomy in that in creates an alternative fluid drainage pathway out of the eye, lowering eye pressure. It differs, however, in that a small drainage tube is inserted into the front chamber of the eye and attaches to a plate that sits underneath the white of the eye.


The tube creates a passage for fluid to from within the eye, into a bleb that forms over the attached drainage plate. Often the tube is partially obstructed by the surgeon, using a stent or an external tying suture, to prevent the eye pressure becoming too low.


Tube shunt glaucoma drainage surgery is an option in advanced glaucoma, or where other treatments and surgeries have failed. It usually takes 1 to 2 hours to perform the procedure, under general or local anaesthesia.

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