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Open-Angle Glaucoma

Of the several types of glaucoma that are found to occur, open angle glaucoma is the one most likely to develop – around 90% of glaucoma cases are of the open angle type in a Caucasian population.  Asians are more likely to develop the Closed-Angle variety.

Glaucoma is an eye disease that affects the optic nerve that takes the messages received by the retina and transmits them to the brain.

Open angle glaucoma is an insidious form of glaucoma in that it develops extremely slowly, with few obvious signs or symptoms, and can proceed to a state where vision is severely affected, even lost altogether.

What is scary is that for a patient to realise that their vision is affected by glaucoma, they will need to lose approximately 60% of the optic nerve for it to make an impact on their perception.  THIS IS TOO LATE!  Regular eye testing will find glaucoma in the early stages when treatment is the most effective.

The eye has many components working in harmony to give us sight.

Behind the cornea at the very front of the eye is an aqueous fluid that fills the gap between it and the iris. The fluid needs to be replenished meaning that it also has to drain away – it does this by passing through a very fine strip of mesh called the trabecular meshwork. The mesh is located at the join between the inside of the cornea and the ciliary muscles holding the eye lens.

It’s the angle between the cornea and the iris being up to 45 degrees where the mesh is located that gives this particular type of glaucoma its name. (If the angle is reduced to the state where the iris comes in to contact the cornea, thereby preventing drainage and immediate and painful increase in pressure, then that type of glaucoma is called a closed angle glaucoma)

If the fluid does not drain away correctly, then there is a build up of pressure (called intra ocular pressure or IOP) in the eye, which leads to degeneration of the optic nerve.

How to detect open angle glaucoma

It’s not easy!

It’s not called the “silent thief of sight” for nothing – an open angle glaucoma, since it doesn’t produce the pain that the closed angle glaucoma does, may go entirely unnoticed as it develops, to the stage where vision is seriously under threat.

The most effective way to detect an open angle glaucoma is by means of regular eye examinations carried out by an eye doctor such as an optometrist or ophthalmologist.
Both professionals carry out screening for glaucoma by measuring intra ocular pressure (IOP) with a tonometer, one type of which introduces a puff of air on to the eye. The machine measures the eye pressure by ascertaining how light reflections are changed by the air hitting the eye.  Another type of tonometer is called the Goldmann – this requires an anaesthetic as the instrument very gently touches the front of the eye.
In addition the rear of the eye and particularly the optic nerve will be examined to check for rim appearance and changes in blood vessels.

Treatment

Management rather than treatment is the course of action to be undertaken, beginning with taking steps to reduce intra ocular pressure. Eye drops, sometimes more than one type will control up to 90% of glaucoma.

Inevitably the use of medications can produce side effects, which on occasion persuade the patient to forego treatment, which is a serious overall problem in the management process – it’s important that the patient discuss any side effects with their practitioners as it is often a simple matter of change of prescription or mode of application.

Increasingly surgery is being utilised to perform very small changes to drainage of the meshwork to alleviate eye pressure.

Overall early diagnosis means early treatment, which means better outcomes.

About the Author

Dr Jim Kokkinakis (Optometrist) graduated in 1983 from the Optometry School University of NSW. He is currently a Senior Lecturer there and regular speaker to both Optometrists and Ophthalmologists in Australia and Internationally. He has a specialist clinical practice in the Sydney CBD with interests in Eye Strain, Computer Vision problems, Treatment of Eye Diseases and complex Contact lens Fittings.

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