Glaucoma

What is Glaucoma?

When the pressure inside the eye (IOP) rises above 21, this is above the “normal range”.  Eight percent of the normal population have pressures above 21 when we take single measurements. This measurement needs to be calibrated by the central corneal thickness.

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How do we diagnose glaucoma?

Glaucoma is diagnosed when there is damage to the optic nerve at the back of the eye.  The retina thins as glaucoma progresses, leading to a characteristic appearance of the nerve in severe cases, called "cupping".  

 

What causes Glaucoma?

We do no know why this damage occurs.    We measure IOP because raised pressure is one risk factor for glaucoma.  The higher the IOP, the more likely a patient will develop glaucoma.  In most patients, damage from glaucoma takes years to develop.

 

Other risk factors are family history, genetics, age, high blood pressure, steroid use, sufferers of migraines or cold hands, diabetes, and eye injury.  Inflammation, bleeding, protein production, and pigment also can raise the intra-ocular pressure.

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Symptoms of Glaucoma.

Most patients with glaucoma have no symptoms.  Glaucoma attacks peripheral vision (side vision) first.  You will not notice loss of peripheral vision, because the brain is very good at filling in the black gaps.  Without effective treatment, severe glaucoma advances until the first thing the patient notices is blindness.

 

How do we monitor glaucoma?

The most accurate way of detecting and monitoring glaucoma is by measuring the optic nerve.  Specifically, we wish to know the thickness of the nerve fibre layer, which makes up the centre of the nerve.  As glaucoma attacks, this layer is gradually thinned, leading to a large central “cup” forming in the centre of the nerve.

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The best way to monitor the nerve and measure this damage is with advanced anatomy scanners such as the OCT (optical coherence tomography).  Another anatomical measurement is the thickness of the nerve fibre layer in the macula, also measured on the OCT machine.  OCT is improving the management of patients with glaucoma because of the accuracy of measurement, and the ability to compare tests over time.  OCT allows us to detect very early change in the optic nerve.  We have been able to take these advanced measurements for 15 years now.  This means that patients with glaucoma can now have long-term anatomical measurements of their optic discs and macula, so detection of progression is much easier than in the past.

 

We also measure the visual fields, because the peripheral vision is affected in advanced cases. Visual field tests are most useful for established glaucoma, and they reflect how the glaucoma is actually affecting your peripheral vision.

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What is ocular hypertension?

When the IOP is elevated, and there is no nerve damage, we call this “Ocular hypertension”. Patients are usually observed without treatment, because the risk of developing glaucoma in 5 years is low.

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How is Glaucoma treated?

When there is obvious damage to the nerve, we diagnose glaucoma, and commence treatment.  Once treatment is started, it will need to continue for the rest of your life.  Once present, glaucoma never goes away. 

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We treat glaucoma by lowering the intra-ocular pressure, the IOP.  We do this with topical drops, laser, tablets, and surgery.  

 

Glaucoma is related to raised IOP.  However, there are some patients with “normal pressure glaucoma” who have damage to the nerve but still have normal pressures.  These patients may be having pressure spikes during the night, or there may be other factors causing glaucoma, such as migraines or poor blood supply.

 

In the past most patients were treated with drops.  Nowadays, many more patients are being offered Laser treatment called "Selective laser trabeculoplasty", or SLT.  This is because a high quality randomised controlled trial called the LIGHT study has shown long term results of benefits from laser over topical drop therapy.

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Modifying your treatment over time.

Most patients do not lose vision from glaucoma.  

 

Initially we determine your "base-line pressure", against which we will compare future IOP readings.  The treatment pressure varies for each patient, depending on many factors.  For some patients, an IOP of 20 will be safe.  For others, 15 may be too high.  To determine your “safe” level, we take multiple readings of the IOP, measurements of the optic nerve, and visual fields.

 

Only by comparing past tests can we detect any progression of the disease.  If there is progression, then we need to change treatment.

 

IOP varies constantly throughout the day.  When we measure IOP in the clinic, it represents just one moment of the day.  We understand that IOP goes up and down, and is affected by many things.  We cannot measure the IOP constantly.  The more frequently we measure IOP, visual fields and disc nerve thickness, the better our information will be.  Field tests are usually repeated every 6-12 months, and disc analysis every 1-2 years.

 

Once treatment is started or changed, you need more frequent review to determine whether the IOP is responding to treatment.

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Most patients with glaucoma are managed successfully by their community optometrist with a visit every 6 months.  This visit should include IOP measurement, OCT disc and macula scans, visual field assessment, treatment check and a general eye check.