Definition and Classification
What is glaucoma?
According to the World Health Organisation glaucoma is the most common cause of irreversible blindness worldwide. In Singapore, it accounts for 40% of blindness.
It is an eye disease which results in damage to the optic nerve, the delicate nerve that carries visual impulses from the eye to the brain.
Glaucoma damage is irreversible and if severe, can lead to visual field narrowing (tunnel vision) and blindness. As most cases of glaucoma are not associated with any obvious symptoms, this dangerous eye condition is often underdiagnosed, or diagnosed too late.
Hence, glaucoma is often called “the silent thief of sight”.
What age group does glaucoma affect?
Glaucoma can present at all ages, in the newborn (congenital glaucoma), in young adults (juvenile glaucoma) and in the elderly.
The risk of having glaucoma increases as we age, especially from the age of 40. In Singapore, glaucoma affects about 3% of those aged over 40. In those aged over 70, glaucoma is present in about 10%.
Types of Glaucoma
There are many types of glaucoma, but there are two main types: Open Angle Glaucoma (OAG) and Angle Closure Glaucoma (ACG). OAG is more common. However, ACG can be more visually destructive, as it often involves higher eye pressures which build up more rapidly. Singapore has one of the highest prevalence of ACG, where it accounts for more than one third of all glaucoma.
Secondary glaucoma can also arise in patients with a dense cataract, previous eye injury or other eye diseases like iritis (inflammation of the eye). Prolonged use of medications such as steroids in the form of oral tablets, ointments/creams, or inhalers can also result in glaucoma.
The majority of glaucoma patients have eye pressures exceeding 21 mmHg. However, patients who have a type of glaucoma called Normal Tension Glaucoma can have nerve damage even when the eye pressure is in the “normal” range of below 21 mmHg.
In some populations, up to 30 to 50% of patients may have at least one first degree relative with glaucoma.
The following groups of people and risk factors have been associated with an increased risk of glaucoma.
• Women
• People over the age of 40
• Asian, Afro-Caribbean and Hispanic ethnicity
• Extremely low or extremely high blood pressure
• High myopia (short-sightedness) or high hyperopia (far-sightedness)
• High intraocular pressure
• Any family history of glaucoma, i.e. blood relatives who have had glaucoma
• Diabetes
• Steroid/cortisone use through medications or creams
• Sturge-Weber Syndrome
• Any previous eye injury or surgery
• Eye conditions such as Aniridia, Dense cataracts and Congenital cataracts, thin corneas, Axenfeld-Rieger Syndrome, Fuchs heterochromic iridocyclitis, Posner-Schlossmann Syndrome, Iridocorneal Endothelial Syndrome, Retinal detachment, Intraocular tumours, lens disorders, eye inflammation such as uveitis, some other eye conditions
• Systemic conditions that may cause inflammation in the eye such as Herpes, HIV, Syphilis, Mumps, Rubella
Symptoms of glaucoma
In cases where the eye pressure is extremely elevated, some glaucoma sufferers may experience symptoms such as eye redness and pain, blurring of vision, halos around lights, or unilateral headaches that may be associated with nausea and vomiting.
However, the majority of glaucoma patients do not suffer any symptoms at all in the early to moderate stages. As glaucoma only affects peripheral vision at first, many people do not notice it, and may only realise that they have a problem with their vision when it spreads inwards and affects their central vision. In many cases, this narrowing of visual acuity takes place over many years. By this stage, the disease is already very advanced and the damage done is irreversible. Hence, glaucoma is known as “the silent thief of sight”. It is therefore absolutely essential to diagnose and treat this condition as early as possible, before significant damage is done to vision.
How is Glaucoma detected?
Glaucoma is traditionally diagnosed and monitored with the help of visual field (VF) tests. However, these tests are not able to detect glaucoma in its early stages. Recently many new imaging devices have become available that can help to detect glaucoma at an earlier stage. These include the Heidelberg Retina Tomograph (HRT) and Optical Coherence Tomography (OCT). Both of these devices can help detect glaucoma up to five to seven years earlier than traditional VF tests.
Patients can therefore be started on treatment earlier so as to prevent any damage to their vision. This way, they stand a better chance of maintaining good vision until a ripe old age. In addition to enabling diagnosis, the HRT, OCT and VF tests are also essential for monitoring the stability of the glaucoma. Regular monitoring with these tests at the eye clinic will enable the glaucoma eye specialist to better decide if they need to modify treatment as the disease progresses.
Treatment options in Glaucoma
Whatever the type of cause of glaucoma, currently all treatments are aimed at decreasing the eye pressure to a safe level, to reduce damage to the optic nerve. The type of treatment required depends on the type and severity of glaucoma present. Treatment can include laser therapy, eye surgery or the daily administration of medication through eye drops. Glaucoma is a chronic condition. That is to say that it cannot be cured, it can only be treated to manage further loss of vision. Therefore lifelong monitoring by an ophthalmologist specialising in glaucoma is essential.
What are the symptoms?
Glaucoma, in most cases, does not have any obvious symptoms. In other words, even if you have glaucoma, you may not be aware of it.
However, a condition called ‘acute angle closure’ is symptomatic and can lead to glaucoma (specifically a type of glaucoma we call primary angle-closure glaucoma).
If you develop acute angle closure you will notice aching pain which does not go away, a red eye and blurred vision. These symptoms are often quite severe and develop over a period of hours. Most people with these symptoms will end up going to a hospital and seeing an eye doctor. Unlike other glaucomas which may take years to cause damage to the optic nerve, acute angle closure attacks cause immediate and permanent damage to the optic nerve and should be regarded as a medical emergency. If you experience them you should go to an emergency room and seek treatment from an ophthalmologist as soon as possible.
Why is the eye pressure important?
Glaucoma tends to get worse over time.
When we manage patients with glaucoma, the studies have shown that if we lower the pressure within the eye (you may hear your doctor refer to this as intraocular pressure, or IOP) then it can slow down the deterioration of the optic nerve.
In addition, if you have high eye pressure it makes you at increased risk of developing glaucoma in the first place.
Do I need to be screened for glaucoma?
Generally speaking we do not screen patients for glaucoma since this has not been shown to be effective in reducing glaucoma-related blindness.
However, if you have first degree relative (parent, sibling or offspring) who has glaucoma and if you are aged over 40 years then it would be worth getting your eyes checked for glaucoma.
Many opticians around Singapore can do this or you can get referred via the polyclinic of GP to see an eye specialist.