Glaucoma Care, Sydney
Early detection, monitoring and treatment to help protect your vision
Glaucoma Assessment and Management
Glaucoma is one of the leading causes of irreversible blindness worldwide. More than 300,000 Australians are estimated to be living with glaucoma. Approximately half do not know they have it, meaning that around 150,000 people may have an eye disease capable of causing permanent vision loss without experiencing any obvious warning symptoms.
Glaucoma Australia estimates that around 1 in 50 Australians will develop glaucoma during their lifetime. The prevalence rises sharply with age, from approximately 1 in 200 people at age 40 to around 1 in 8 by age 80.
At Eye and Retina Specialists, glaucoma assessment combines information about family history of glaucoma, optic nerve examination, OCT imaging, visual field testing, measurement of eye pressure, corneal thickness and, gonioscopy. These findings are interpreted together to determine assess the risk for glaucoma , determine how advanced it is and if treatment is required. We use advanced glaucoma progression analysis software to monitor for progression to reduce the risk of vision loss.
What is Glaucoma?
Glaucoma is a chronic disease that causes progressive, irreversible damage to the optic nerve. The optic nerve is the main supply of visual information from the eye to the brain where it is processed and interpreted.
Glaucoma is not simply “high pressure in the eye.” It is a group of diseases that progressively damage the optic nerve, which carries visual information from the retina to the brain. Raised intraocular pressure (IOP) eye pressure is the most important treatable risk factor, but glaucoma can develop when pressure readings fall within the usual statistical range. Conversely, some people with elevated pressure never develop optic nerve damage.
Vision already lost through glaucoma cannot currently be restored. The purpose of diagnosis and treatment is therefore to identify the disease before substantial functional loss has occurred and to preserve the vision that remains.
The optic nerves carry visual information from each eye to the brain. At the optic chiasm, some fibres cross allowing each side of the brain to receive information from both eyes
What happens to the optic nerve in glaucoma?
The optic nerve contains approximately one million nerve fibres formed by retinal ganglion cells. These fibres collect visual signals from across the retina and transmit them towards the brain. At the optic chiasm, some fibres from each eye cross to the opposite side, allowing each cerebral hemisphere to receive visual information from both eyes.
Glaucoma causes progressive death of retinal ganglion cells and loss of their nerve fibres. This can be seen clinically as thinning of the retinal nerve fibre layer and loss of the neuroretinal rim around the optic nerve.
The pale depression at the centre of the optic nerve is known as the cup. As glaucomatous tissue is lost, the cup usually enlarges and the remaining rim becomes thinner or develops focal notching. Importantly, the outer boundary of the optic disc does not become larger. It is the cup within the disc that expands as neural tissue is lost.
A large cup does not automatically mean glaucoma. Some healthy people have naturally large optic nerves and correspondingly large cups. Others have relatively small discs in which significant tissue loss may be less visually dramatic. Cup-to-disc ratio therefore needs to be interpreted alongside disc size, rim configuration, nerve fibre layer appearance, OCT imaging, visual field results and evidence of change over time.
Glaucoma progressively enlarges the optic nerve cup and thins the surrounding neuroretinal rim
Glaucoma Symptoms
In most cases, people with the early stages of glaucoma are asymptomatic and unaware they have the condition.
Early damage often affects parts of the peripheral visual field rather than the centre. The other eye may compensate, and the brain may fill in missing information instead of presenting the patient with a clearly visible black area. A person can therefore continue to read the smallest letters on an eye chart while already having clinically important loss elsewhere in the visual field.
With more advanced disease, patients may have difficulty seeing objects approaching from the side, finding items in clutter, navigating stairs, moving in dim lighting or detecting pedestrians and vehicles when driving.
Severe constriction sometimes described as “tunnel vision” is generally a late manifestation, not the way early glaucoma usually presents. If untreated, it can eventually cause loss of the central vision.
What Causes Glaucoma?
There is substantial evidence that there is a genetic component to the development of glaucoma. A number of genes implicated in the pathogenesis of glaucoma have been identified in recent years. Those people with a first degree relative who has been diagnosed with glaucoma should have their eyes regularly screened for this condition.
As mentioned earlier, high intraocular pressure is the major risk factor for the development of glaucoma. Other factors such as a thin central cornea may also play a role. There are numerous secondary causes of glaucoma, including a history of blunt ocular trauma among others. Our specialists can discuss this with you further.
Raised Intraocular Pressure is a Risk Factor
The eye continuously produces clear aqueous fluid. This fluid circulates through the front of the eye and normally drains through the trabecular meshwork within the angle between the cornea and iris.
If resistance to outflow increases, the pressure within the eye may rise. The level of pressure that an optic nerve can tolerate varies considerably between people. There is therefore no single pressure that is automatically safe or harmful for everyone.
Some patients have ocular hypertension: pressure above the usual population range without corresponding optic nerve or visual field damage. Their risk of developing glaucoma depends on several factors, including the degree of pressure elevation, age, corneal thickness, optic nerve appearance and family history. Other patients develop normal-tension glaucoma despite intraocular pressure readings within the normal range.
How is Glaucoma Diagnosed?
There is no single test to diagnose glaucoma. Rather, a combination of tests and investigations are needed. These can include measures of the central cornea thickness, IOP measurement, clinical optic nerve assessment, peripheral visual field testing, and optical coherence tomography (OCT) to evaluate the retinal nerve fibre layer thickness. Our specialists use these various parameters to detect early signs of glaucoma and recommend treatment at an early stage, before significant irreversible damage occurs.
Examination of the optic nerve
The optic nerve is examined stereoscopically, usually through a dilated pupil. Assessment includes the disc size, cup, neuroretinal rim, retinal nerve fibre layer, symmetry between the two eyes, blood vessel configuration and the presence of optic disc haemorrhages.
Focal rim notching and corresponding nerve fibre layer defects are important features.
Intraocular pressure measurement
Intraocular pressure measurement is important to diagnose and monitor response to glaucoma treatment. Ocular pressure varies during the day and between visits.
Corneal thickness
Central corneal thickness is measured using pachymetry. A particularly thick or thin cornea can affect the interpretation of measured pressure and may also influence the patient’s overall risk profile. The Ocular Hypertension Treatment Study (OHTS) demonstrated that an unusually thin central cornea is an independent risk factor for developing glaucoma, apart from the effect on intraocular pressure assessment.
Gonioscopy
Gonioscopy uses a small mirrored contact lens placed against the anaesthetised cornea while the eye is examined at the slit lamp. It permits direct inspection of the drainage angle, which cannot otherwise be seen because of internal reflection within the cornea.
Gonioscopy distinguishes open-angle from narrow- or closed-angle disease and may reveal excessive pigmentation, pseudoexfoliation, inflammation, abnormal blood vessels, previous trauma or peripheral anterior synechiae.
Visual field testing
Automated perimetry measures visual sensitivity at numerous locations away from the centre of fixation. Early glaucoma may produce a nasal step, paracentral defect or arcuate pattern corresponding to the anatomy of the retinal nerve fibre layer. Visual field testing is important in the diagnosis and monitoring of glaucoma.
OCT imaging
Optical coherence tomography measures the retinal nerve fibre layer around the optic disc and the ganglion cell layers within the macula. These tissues contain the cells and axons damaged by glaucoma.
OCT can detect structural loss before a patient notices symptoms and sometimes before a repeatable visual field defect is apparent. OCT progression analysis is clinically important for longitudinal assessment over time, to monitor for signs of glaucoma development or progression.
Optical coherence tomography (OCT) imaging is an part of a glaucoma assessment and monitoring
Types of Glaucoma
Primary open-angle glaucoma is the most common form. The drainage angle is physically open, but resistance within the drainage pathway is sufficient to contribute to progressive optic nerve damage.
Normal-tension glaucoma produces the characteristic structural and functional changes of glaucoma despite pressures that remain within the usual statistical range.
Angle-closure disease occurs when the peripheral iris narrows or obstructs access to the trabecular meshwork. Angle closure may be intermittent or chronic and entirely asymptomatic, or it may present as an acute painful attack.
Secondary glaucoma can develop because of another ocular or medical problem. Causes include inflammation, trauma, abnormal new blood vessels, pseudoexfoliation, pigment dispersion, previous surgery and corticosteroid exposure.
Congenital and juvenile glaucomas are uncommon but can occur in infants, children and young adults. It is estimated that approximately 1 in 10,000 babies is born with glaucoma.
How is Glaucoma Treated?
The aim of treatment for glaucoma is to reduce the rate of progression of the disease, and to maintain good vision throughout the patient’s life. Treatment may be in the form of eye drops to lower the intraocular pressure, laser treatment, surgery, or a combination of these options. Unfortunately, once vision has been lost from glaucoma it cannot be restored, so early diagnosis and treatment is imperative. Our specialists will individualise your care and recommend the treatment most suited for your case.
