Glaucoma

Glaucoma

Early detection of glaucoma is critical for preventing vision loss, but there are often no obvious symptoms in the early stages of the disease. OKKO Eye Specialist Centre specialises in early testing, and will help you manage the diagnosis and treatment of glaucoma.

What is glaucoma?

Open Angle Glaucoma is a condition in which the optic nerve, the structure responsible for transmitting information from the eye to the brain, becomes progressively damaged.

Glaucoma causes a gradual loss of the optic nerve fibres, leaving the eye and vision slowly affected over time. Peripheral vision is usually affected before central vision, and in advanced glaucoma patients can be left with only "tunnel vision".

Causes and symptoms

Damage to the optic nerve is most commonly secondary to high pressure within the eyeball, which is known as intraocular pressure. Intraocular pressure is determined by the eye's production of fluid, and the drainage of this fluid into the blood stream via the eye’s trabecular meshwork. The production-drainage ratio is normally strictly auto-regulated by the body. In OAG, this balance is not adequately maintained, and intraocular pressure increases as a result.

Other risk factors for glaucoma include older age, a positive family history, diabetes, higher short-sightedness and previous trauma to the eye.

Testing and diagnosis

Early detection is critical for preventing severe vision loss, so it is important that you do not wait for symptoms before getting tested for glaucoma.

Glaucoma testing may include a non-invasive examination of the optic nerve using a special microscope and scanning devices, a measurement of the intraocular pressure, and a computerised test to formally measure peripheral vision.

Diagnosis can be difficult in the early stages, and multiple tests are usually required. In cases where a diagnosis cannot be definitively made, your eyecare practitioner may elect to monitor you closely before deciding to start treatment.

Treatment

Current treatment options for glaucoma attempt to lower intraocular pressure to prevent further progression, but they do not reverse any optic nerve damage or vision loss that has occurred. This is why early detection is so important.

The current first-line treatment for glaucoma is eye drops. Most glaucoma medications are safe to use and have minimal ocular and systemic side-effects. Sometimes more than one drop is required to stabilise the intraocular pressure, and dosing varies from once a day to three times a day.

Sometimes, more than one type of anti-glaucoma medication is required to adequately control your intraocular pressure. This kind of treatment is usually an ongoing commitment for life.

Other treatment options for glaucoma include laser and, in more advanced cases, surgery.

Selective Laser Trabeculoplasty (SLT) is a special laser applied to the trabecular meshwork in an attempt to improve the outflow of aqueous fluid.

SLT is often considered if a patient has had a suboptimal response to anti-glaucoma medication or is not tolerating the eyedrops. Laser is very safe and painless, however more than one treatment may be required for maximal effect. The efficacy of SLT may also reduce over time, and some patients still require ongoing medical therapy despite SLT treatment.

Surgery is usually only considered for treatment of advanced glaucoma, when neither medical therapy nor laser has been sufficient in stopping progressive optic nerve damage and/or vision loss.

There are numerous surgical options for OAG, including trabeculectomy and insertion of a drainage implant or shunt. When necessary, these surgeries are performed by our trained ophthalmologists who specialise in glaucoma.

Yes. The broadest classification of glaucoma separates Open Angle Glaucoma from Angle Closure Glaucoma (ACG).

In ACG, the normal flow of aqueous becomes increasingly impeded due to underlying anatomical variation and/or cataract formation. In an acute ACG attack, the drainage channel is completely blocked and there is a rapid increase in intraocular pressure accompanied by a red painful eye. Your eyecare practitioner can screen you to determine if you are at risk of developing ACG in the future.

Additionally, OAG sometimes occurs secondary to other ocular conditions. These include Pigment Dispersion Syndrome, Pseudoexfoliation Syndrome and inflammatory eye disease (uveitis). Use of steroid eyedrops and trauma to the eye can also cause secondary open angle glaucoma.

Diagnosing OAG can be difficult in the early stages, and multiple tests are usually required. In cases where a diagnosis cannot be definitively made, your eyecare practitioner may elect to initially monitor you closely before deciding to start treatment.

Eye Examination
A measure of your visual acuity on a letter chance is made, and your eyecare practitioner will also examine the optic nerve head at the back of the eye using a slit lamp microscope. The slit lamp and/or a special contact lens (gonioscopy lens) can also be used to screen people for risk of angle closure glaucoma.

Tonometry
Tonometry is the measurement of intraocular pressure. There are several instruments available to measure intraocular pressure, such as applanation tonometers, non-contact (puff) tonometers and rebound tonometers. Intraocular pressures are generally higher in people with thicker corneas, and lower in those with thin corneas.

It is well recognised that intraocular pressures can vary by about 3-6mmHg over the course of a day, a phenomenon known as diurnal variation. Intraocular pressures are highest in the early hours of the morning, and lowest at the end of the day. Your eyecare practitioner may recommend a Drink Water Test to evaluate the extent of diurnal variation. This test involves drinking about 1L of water in order to simulate peak intraocular pressure. Pressure measurements are then taken every 15 minutes for an hour.

Visual Field Testing
Visual fields are a formal measurement of the peripheral vision. They are used to determine if there has already been visual field loss from glaucoma, and to monitor glaucoma progression over time.

Initially, visual fields can be hard to perform accurately. Performance improves significantly on repeat testing. You may need to do 2-3 visual field tests to generate reliable, repeatable results for interpretation by your eyecare practitioner.

Retinal Nerve Fibre Layer (RNFL) Analysis
Retinal Nerve Fibre Layer (RNFL) analysis non-invasively and quantitatively measures the thickness of the nerve tissue around the optic disc. Like visual field testing, RNFL analyis is used to both help in the diagnosis of glaucoma and as an aid in monitoring response to treatment.

Intraocular pressure is currently the only modifiable factor in managing glaucoma. Treatment options aim to reduce intraocular pressure to a predetermined target therapeutic pressure. Optic disc damage and vision loss that has already occurred due to OAG cannot be reversed. Early detection is critical for preventing these changes from happening.

Medical Therapy
The mainstay treatment for OAG is anti-glaucoma eyedrops. There are several different classes and subtypes of glaucoma medications. The drops either reduce the production of aqueous fluid from the ciliary body or increase outflow via the trabecular meshwork.

Most glaucoma medications are safe to use and have minimal ocular and systemic side-effects. Dosing varies from once a day to three times a day. Your eyecare practitioner will discuss in detail with you any known adverse drug reactions and or potential interactions with your other medications prior to commencing treatment.

More than one type of anti-glaucoma medication is sometimes required to adequately control the intraocular pressure. Medical therapy will usually be an ongoing commitment for life.

Selective Laser Trabeculoplasty (SLT)
Selective Laser Trabeculoplasty (SLT) is a special laser applied to the trabecular meshwork in an attempt to improve the outflow of aqueous fluid.

SLT is often considered if a patient has had a suboptimal response to anti-glaucoma medication or is not tolerating the eyedrops. Laser is very safe and painless, however more than one treatment may be required for maximal effect. The efficacy of SLT may also reduce over time. Some patients still require ongoing medical therapy despite SLT treatment.

Glaucoma Surgery
Surgery is usually considered for treatment of advanced OAG, when neither medical therapy nor laser has been sufficient at stopping progressive optic nerve damage and/or vision loss. There are numerous surgical options for OAG, including trabeculectomy and insertion of a drainage implant or shunt. These surgeries are performed by ophthalmologists specialising in glaucoma.

Early OAG is generally asymptomatic, and progression is fortunately slow. However, as optic nerve damage progresses people may start to notice small areas of mild blur in their peripheral vision or just adjacent to their central vision. If treatment is not started, the visual field can continue to constrict. In advanced glaucoma, patients are left with ‘tunnel vision’. 

Do not wait for symptoms before getting tested for glaucoma. Vision loss from glaucoma is often insidious and cannot be reversed, hence it is often called the ‘sneak thief of sight’. Early detection can potentially preserve vision over the long term.

Open angle glaucoma (OAG) is a type of optic neuropathy in which there is progressive damage to the optic nerve, and the nerve tissue in the optic disc becomes increasingly thinned over time. Vision gradually becomes affected, with peripheral vision generally being affected before central vision.

Damage to the optic nerve head in OAG is most commonly secondary to high pressure within the eyeball (intraocular pressure), although this is not always the case.

Some people have elevated intraocular pressures (defined as greater than 21mmHg) but with no evidence of damage to the optic disc or their vision. These patients have ocular hypertension. They may be more at risk of developing open angle glaucoma in the future and require close monitoring. Conversely, there are people who have normal intraocular pressures (10 to 21mmHg) but still show progressive optic disc damage and/or vision loss. These patients have a condition known as normal tension glaucoma. Currently, it is believed that normal tension glaucoma is caused by poor blood flow through the optic nerve.

Intraocular pressure is primarily determined by two things – production of fluid (aqueous) by the ciliary body, and drainage of fluid into the blood stream via the trabecular meshwork.

The production-drainage ratio is normally strictly auto-regulated by the body. In OAG, this balance is not adequately maintained (i.e. too much production or not enough drainage) and intraocular pressure increases as a result.

There are several recognised risk factors that can increase the likelihood of someone developing OAG. These include:

  • age (OAG is more likely in people over 40 years of age)
  • family history of glaucoma
  • ocular hypertension
  • African and Latino heritage
  • thinner cornea (the membrane covering the front of the eye)
  • diabetes
  • high short-sightedness
  • previous ocular trauma
  • extremely high or low blood pressure