Glaucoma

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
• Headache
• 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:

• Age
• 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.