The secret thief of sight.
Glaucoma is the leading cause of irreversible vision loss in developed countries (according to the World Health Organisation), with 2 in every 100 Australians developing the disease.
Half of all Australians with the disease remain undiagnosed. This alarming figure is likely due to the fact that glaucoma often has no obvious symptoms until the late stages of the disease when the patient has already lost most of their vision. This is why this disease has been dubbed ‘the silent thief of sight’.
Unfortunately, the condition can often be missed in its early stages. Unless specialised equipment is used by an optometrist or ophthalmologist to thoroughly examine the eye, it can be very difficult to make a correct diagnosis.
Glaucoma is not a “normal” part of ageing, like reading glasses or cataracts. Glaucoma is a serious condition that requires early diagnosis and treatment to avoid permanent vision loss.
The good news is, with early diagnosis and appropriate treatment, any further vision loss can be slowed down or prevented completely.
By the time you notice symptoms, up to 50% of your retinal nerves may already be lost. There is no current treatment for reversing this damage, not even surgery.
Glaucoma is the name given to a group of sight threatening eye diseases in which the optic nerve at the back of the eye is damaged or destroyed. The optic nerve is responsible for relaying the visual information of what you are seeing, back to the brain. In the most common form of this disease, the destruction of the optic nerve occurs gradually over time and if left untreated can lead to blindness.
There are many forms of glaucoma, with primary open angle glaucoma being the most common type. Other types include angle-closure glaucoma, secondary glaucoma and congenital glaucoma.
Primary open angle glaucoma (POAG)
This is where the angle (or space between the cornea and the iris of your eye) is open as normal, but the intraocular fluid (or aqueous humour) cannot filter out of the eye as fast as it is being produced, leading to an increase in intraocular pressure (IOP). This pressure gradually damages the optic nerve at the back of the eye.
Acute angle closure glaucoma
This is also called Closed-angle (or Narrow-angle) glaucoma. It occurs when the space between your cornea and iris is narrow, impeding the outflow of intraocular fluid. Intraocular pressure can build up gradually or suddenly, in the case where the angles close or the pupil becomes blocked by your natural lens. This condition is more common in Asians, due to their having a naturally shallow front chamber in their eyes. Certain medications can also increase the risk of developing this disease. It can also happen during an eye exam, when the pupils are dilated to provide a better view of the back of your eye.
This rare condition occurs in less than 1 in 10,000 babies and is diagnosed at birth or during the first year of life. It has a genetic cause, which causes the drainage apparatus of the eye to malfunction. It is treated by surgery to facilitate drainage.
This is when the disease is caused by another condition or disease, or trauma, e.g:
- Pigment from the back of the iris clogs up the drainage system – also called the trabecular meshwork – (like leaves in a gutter). This is called Pigment dispersion syndrome (or PDS). It is usually managed with eye drops.
- Exfoliated cells from the front of the natural lens in your eye can also clog up the drainage channels. This is called Pseudo-exfoliation syndrome (or PXF).
- New blood vessels (neovascular changes) can occur in diseases such as diabetes or central retinal vein occlusion. These abnormal vessels can grow in the iris and block off the drainage channels completely. This is particularly difficult to manage.
- Uveitis is an inflammation of the iris of your eye. Inflammatory cells can also silt up the delicate drainage system of the eye, leading to uveitic glaucoma.
- Blunt trauma, such as a cricket ball to the eye, can cause the drainage system to rip open. As it heals, it scars and prevents outflow of intraocular fluid.
Causes and risk factors
While the exact mechanism of glaucoma is not fully understood, it is clear that some eyes are vulnerable to damage from intraocular pressure – even normal pressure. This is a complex and multifactorial disease and it is often better to look at the risk factors.
Your optometrist will ask you about these during the course of your routine eye examination. The baseline risk of developing glaucoma is 2%.
If you have a parent with this disease, your risk is about 10%. A sibling with the disease puts your risk up to 10-50%. This means, if you or your siblings are diagnosed with glaucoma, all siblings should be thoroughly checked for the disease as there is a high chance they will also have it.
This disease is much more common as you get older – 6 times more common if you are over 60. 1 in 8 people over 80 will develop this disease.
African-American race, POAG is 6-8 times more common in this group. Asian eyes are more likely to develop angle-closure glaucoma (which is rare in Caucasian eyes).
Central corneal thickness
A thinner than normal cornea can be a reliable indicator of vulnerability to damage from intraocular pressure.
This means intraocular pressure above normal and is not the same thing as glaucoma. It is simply a risk factor just as a high cholesterol level is a risk factor for heart disease.
What’s a ‘safe’ intraocular pressure?
This is a common question from patients visiting their optometrist or ophthalmologist. There is no universally ‘safe’ intraocular pressure level as regards glaucoma risk. This will depend on your unique situation. Ocular hypertension – or intraocular pressure higher than 21mmHg – is not the same thing as glaucoma. An eye with a pressure of 25mmHg (higher than normal) can be otherwise perfectly normal, while another eye with an intraocular pressure of 12mmHg (well within the normal range) can be slowly going blind from glaucoma. This type of POAG is sometimes called ‘normal tension glaucoma’ because the pressure is not higher than average.
Asking what your IOP is will only tell you if you have ocular hypertension or not and will not tell you if you have glaucoma or not. It is true, however, that your risk of developing the disease is higher (10%) if you have ocular hypertension, compared to normal (2%). Many practitioners prefer to call patients with ocular hypertension glaucoma suspects, who require more regular follow up.
It is critical that glaucoma is detected early in order to prevent any sight loss. Glaucoma can occur at any age and you should be screened no later than the age of 40, or 30 if you have a family history of glaucoma or have other risk factors.
Certain equipment is needed for thorough screening, monitoring and treatment of glaucoma. The best way to detect glaucoma early is with regular eye examinations by an optometrist. The Eye Practice offers comprehensive glaucoma screening and includes OCT to screen all patients for this disease.
Is there a cure?
Whilst there is no cure for glaucoma, it can be managed with several different treatment methods. Effective treatment cannot reverse the vision loss, but it can slow down or prevent future loss.
PLEASE READ: The information given under Eye Conditions is of a general nature and is not intended to be advice on any particular matter. Please take the appropriate Optometrical advice before acting on any information given under Eye Conditions of The Eye Practice web-site.