Glaucoma is the name given to a group of eye diseases in which the optic nerve is slowly destroyed. It is often, but not always, associated with increased eye pressure. When glaucoma is not related to increased eye pressure the damage to the optic nerve may be a result of poor blood supply to the nerve, a weakness in the structure of the nerve and/or a problem with the health of the nerve fibres themselves.
Glaucoma is commonly referred to as the “sneak thief of sight”, because often there are no symptoms until permanent damage has occurred. Once vision is lost it cannot be regained, however early treatment can often prevent further loss of sight so early detection is important. If untreated, glaucoma may eventually cause total black blindness.
To understand how high eye pressure can lead to the development of glaucoma, it is important to understand how the eye maintains its healthy structure. A clear fluid called aqueous humour is produced by the ciliary body and flows into the anterior chamber of your eye providing nutrients to the cornea and lens. The fluid then drains out through a sieve-like structure called the trabecular meshwork.
To maintain a healthy pressure within the eye, a small amount of aqueous humour is produced constantly while an equal amount flows out through the trabecular meshwork. If the drainage becomes blocked or the fluid cannot drain adequately then fluid will build up in the anterior chamber. This results in an increase in eye pressure, which in turn, can place pressure at the optic nerve and damage the nerve fibres. This damage is permanent. Therefore treatment is needed to lower the eye pressure and prevent any further damage of the optic nerve.
There are different types of glaucoma each with different causes. However they all share the same problem: a specific pattern of optic nerve damage; often associated with relatively abnormal eye pressure. Impaired vision or blindness often results if undetected and untreated.
Open angle glaucoma: This is the most common type of glaucoma. This condition is usually painless and without symptoms, so a person may not be aware that damage is occurring. In open angle glaucoma, the aqueous fluid cannot flow through the trabecular meshwork and drain properly, causing eye pressure to rise and eventually damage the optic nerve. Damage normally occurs slowly and is progressive.
Acute or Angle-closure glaucoma: This occurs when the iris (the coloured part of your eye) is too close to the drainage angle. In these eyes, which are often small and far sighted, the iris can often be sucked into to drainage angle and block it completely. Since fluid cannot drain from the eye, pressure rapidly builds inside the eye and results in an acute closed-angle attack. Symptoms can include:
- Sudden severe eye pain
- Blurred vision
- Coloured haloes around lights
- Nausea and vomiting
This is a true eye emergency as damage to the optic nerve can occur within hours. Emergency treatment (usually medication and laser) is needed to prevent partial or complete loss of vision.
A chronic form of closed angle glaucoma may occur slowly and without symptoms, sometimes known as narrow angle glaucoma.
Normal Tension glaucoma: This occurs in people with average eye pressures who nonetheless suffer damage to the optic nerve. It is more common than previously considered and is due to increased sensitivity to pressure by the optic nerve.
Childhood glaucoma: This is rare and may start in infancy, childhood or adolescence. It is hereditary and may lead to blindness if not treated.
Congenital glaucoma: This is a form of childhood glaucoma that is usually detected during the baby’s first six months. It is due to a fault in the development of the trabecular meshwork. Surgery is the most effective treatment.
Secondary glaucoma: This is where eye pressure increases due to other eye conditions such as injury, medication, haemorrhage, tumour, inflammation and other conditions which can block the outflow of aqueous fluid.
Although anyone can develop glaucoma, some people have a higher risk. The risk factors include:
- Elevated eye pressure
- Family history of glaucoma
- African or Spanish ancestry
- Farsightedness or nearsightedness
- Past eye injuries
- Thinner central corneal thickness
- Prolonged use of cortisone medication (steroids)
- Systemic health problems, including diabetes, migraine headaches, high blood pressure and poor circulation
Anyone in these higher risk groups should have their first eye check no later than the age of 35. For most people, it is recommended to have an eye check for glaucoma by the age of 40.
Regular eye examinations by your ophthalmologist are the best way to detect glaucoma. During a glaucoma evaluation the following tests may be done:
- Tonometry – to measure your eye pressure
- Gonioscopy – to inspect the drainage angle inside your eye
- An ophthalmoscope is used to view the optic nerve.
- Ocular Coherence Tomography (OCT) – this machine has software that is able to generate images of the optic nerve and the nerve fibre layer (NFL) which results in the detection of structural changes.
- Humphrey Field Analysing – this test is designed to map your visual field to ascertain the level of peripheral or side vision. Each eye is tested separately and your chin is placed on the chin rest while you are instructed to focus on a small orange fixation light in front of you with the eye that is about to be tested. The machine resembles a large concave bowl and the test consists basically of responding every time a white flash of light is perceived on the white background of the bowl.
- Pachymetry – to measure the thickness of your cornea as this may impact on your eye pressure reading
These tests may be repeated routinely to determine if there are any changes over time.
Yes. An early and accurate diagnosis of glaucoma coupled with currently available therapies is the most effective manner in which to preserve the health of the optic nerve and hence, maintain healthy vision. By contrast, those cases that already involve visual field loss, due to optic nerve damage from a late diagnosis, may be treated by the same therapies; however, they would have already sustained permanent and irreversible loss of vision.
Glaucoma can be identified early through the use of specialized analytical equipment. Current imaging software generates images of the optic nerve head and nerve fiber layer (NFL), allowing for the early detection of any structural changes. A specialized software program on Humphrey Field Analyser is also available and can highlight any subtle changes to your peripheral or side vision.
In recent years new techniques of optic nerve imaging have become widely available. The imaging equipment used in our clinic is an Optical Coherence Tomography or OCT. The OCT machine is able to create a contour map of the optic nerve as well as measure the thickness of the retinal nerve fiber layer. This in turn allows for the analysis of any structural changes.
The Humphrey Field Analyzer allows for the monitoring of any changes to your peripheral or side vision. An included function of the Analyzer is a program called SWAP which stands for Short Wavelength Automated Perimetry. SWAP employs a yellow background with a blue flash of light instead of the standard white flash of light on a white background. Testing your visual field in this manner allows the detection of any abnormalities that manifest during the early stages of glaucoma as it is more sensitive to subtle visual field changes than the standard program on the Humphrey Field Analyzer.
Damage to your optic nerve cannot be reversed and there is no cure for glaucoma. Glaucoma can be controlled with treatment, to prevent further damage and loss of sight. Treatment for glaucoma includes: eye drops, laser or surgery.
Glaucoma is commonly controlled with eye drops taken daily. These drops help lower eye pressure by either decreasing the amount of aqueous fluid being produced or by improving the fluid drainage through the trabecular meshwork. The drops can be varied to best suit the patient and the type of glaucoma.
Some eye drops may cause side effects in certain people. You should notify your ophthalmologist if you experience any of the below side effects.
- Stinging & itching which is prolonged
- Red eyes, or redness around your eyes all the time
- Changes in pulse and heart beat
- Changes in energy levels
- Changes in breathing
- Changes in sensation of taste
- Blurred vision
- Change in eye colour
You should never change or stop taking your eye drops without advice from your ophthalmologist. If you are running low on medication then contact our rooms to arrange a new prescription.
Different drugs can interact, including eye drops, therefore it is important to make a list of all your medications and share this with each doctor you see.
Laser may be recommended for different types of glaucoma. In open angle glaucoma laser is used to modify the trabecular meshwork to improve fluid drainage and control eye pressure – this is called trabeculoplasty.
In closed angle glaucoma, the laser creates a hole in the iris, (coloured part of our eye), to improve flow of the fluid to the drainage trabecular meshwork – this called an iridotomy.
Glaucoma Drainage Surgery
Should drops or laser treatment prove unsuccessful, it may be necessary to perform glaucoma drainage surgery. This needs to be done within a hospital and is usually a day procedure. The main options are a Trabeculectomy or a Drainage Valve.
In these procedures a new drainage channel is created through the wall of the eye to allow the aqueous to slowly drain out of the eye.
Recovery time varies and the eye could take up to six weeks to completely settle.
Molteno Valve Surgery
The Molteno valve surgery is an alternative glaucoma drainage operation.
The device operates by bypassing the trabecular meshwork and redirecting the outflow of aqueous humor through a small tube into an outlet chamber, commonly referred to as a bleb. The surgery involves a flow tube being inserted into either the anterior or the posterior chamber of the eye and a plastic saucer is being implanted underneath the conjunctiva to allow redirection of aqueous humor to occur.
With any type of glaucoma, periodic examinations are very important to prevent vision loss. Glaucoma can progress without your knowledge; therefore adjustments to your treatment may be necessary over time.
Risks of Glaucoma Surgery
- Excessive lowering of eye pressure can cause blurred vision for a period of time
- Increase in eye pressure requiring regular visits to the specialist to assess.
- Temporary inflammation inside the eye causing pain and blurred vision.
- An increased risk of developing cataract causing blurred vision
- Gradual closure of the new channel with scar tissue causing failure
- Infection causing blindness
- Bleeding, discomfort or pain in your eye
- Retinal detachment causing loss of vision
- Choroidal effusion causing loss of vision
With surgery the new channel created is usually efficient at draining away the excess fluid; however the underlying problem still exists. That is, the natural drainage passage in the eye is not able to function adequately. If the new passage closes over with scar tissue over time, then glaucoma can progress. It is difficult to predict how long the effect of the treatment will last. It may range from months to years. Regular eye examinations are crucial following this treatment.
Details regarding risks and complications will be provided by your treating ophthalmologist when discussing treatment and proceeding with consent. At this time, your Brisbane Eye Clinic Ophthalmologist will be pleased to answer any queries you may have.