Glaucoma – all you need to know about the second leading cause of blindness
Glaucoma is a serious eye disease that affects eye pressure.
Glaucoma is the world’s second leading cause of blindness1. According to the World Health Organization, around 4.5 million people globally suffer from blindness due to glaucoma. It is estimated that this number will rise to 11.2 million people by 2020. That’s a 149% increase—6.7 million more people who may be at risk of losing their vision to this "silent blinding disease", and they have no idea it's even happening.2 BETTER VISION explains what you should know about this group of eye diseases, eye pressure, and the causes, risk factors, screening methods and treatment associated with glaucoma.
What is glaucoma?
Glaucoma is complex disease with many forms, but in short it can be defined as damage to the nerve connecting the eye to the brain (called the optic nerve) mostly due to eye pressure (intraocular pressure), which influences your visual field and visual acuity.
The risk of getting glaucoma is six times more likely if you are over 60 years old.
To better understand how the optic nerve is damaged, consider the working of the eye:
The ciliary body produces a clear, watery liquid called aqueous humour in the front chamber that provides nutrition to various parts of the eye including the lens, cornea and ocular tissues. This fluid then drains from the eye through a spongy network called the trabecular meshwork and exits through Schlemm’s canal into the blood vessels.
Most commonly, glaucoma affects Schlemm’s canal or the trabecular meshwork, meaning that the aqueous humour can’t leave the eye as usual. Compare this to a cement dam with a blocked overflow – if it’s continuously pumped full of water that can’t drain, pressure will increase, and the dam wall will eventually burst. Similarly, when Schlemm’s canal or the trabecular meshwork is blocked it will cause a buildup of aqueous humour that will affect eye pressure which in turn damages the optic nerve and will influence your vision.
Development of Glaucoma
There are two categories of glaucoma, closed-angle and open-angle glaucoma. Each category is defined by the position of the ocular lens and iris in relation to the trabecular meshwork3, which determines how the aqueous humour is drained from the eye or not.
With closed-angle glaucoma, the angle between the iris and the cornea is either narrowed or blocked, or the trabecular meshwork is damaged, causing a buildup of aqueous humour and a sudden increase in eye pressure. This leads to severe eye pain and it’s considered a medical emergency that must be managed immediately to avoid blindness.
In primary closed-angle glaucoma there’s no identifiable cause of increased eye pressure, and it may just happen because of the way the eye is structured. If there is a secondary cause such as an underlying condition, an injury, inflammation or diabetes mellitus causing a sudden increase in eye pressure, it is described as secondary closed-angle glaucoma.
With open-angle glaucoma, the drainage angle between the iris and the cornea is wide and open, but there is a slow blockage of the drainage canals. The fluid (aqueous humour) passes too slowly through the trabecular meshwork to drain properly, creating a gradual increase in eye pressure that can damage the optic nerve and lead to blindness. The symptoms are not noticed immediately or often not noticed at all.
Open-angle glaucoma is the most common form of this type of eye disease, accounting for at least 90% of glaucoma cases according to the Glaucoma Research Foundation.
As with closed-angle glaucoma, the open-angle form of the disease can be divided into primary and secondary categories:
Primary open-angle glaucoma (POAG)
This category includes forms of glaucoma where there is a slow blockage, and there is no secondary cause of this blockage that can be clearly identified.
POAG risk factors include:
- Increased eye pressure
- Age (60+)
- Genetic factors such as a family history of glaucoma
- Ethnicity – people of Hispanic and African ancestry are at a greater risk for developing POAG4
- People who suffer from nearsightedness (myopia) have an increased risk of developing POAG5
- Diabetes Mellitus
- Use of certain chronic medications
- Sleep apnea
Secondary open-angle glaucoma (SOAG)
In this category, the slow blockage of the drainage canals has a direct cause.
Secondary factors that can lead to SOAG include:
- Use of medication such as cortisone
- Congenital factors that present at or before birth
- Conditions such as pseudoexfoliation (an abnormal accumulation of protein in the eye structures) and pigment dispersion syndrome (leading to pigmentary glaucoma)
- Inflammatory eye disorders (uveitis)
- A mechanical blockage due to an increase in lens thickness (phacomorphic glaucoma)
What impact does glaucoma have on vision?
Apart from a sudden increase in eye pressure and extreme pain experienced in the closed-angle form, glaucoma is often only noticed once it has already damaged the optic nerve and retina. In fact, patients with primary open-angle glaucoma rarely experience visual symptoms, at least during the onset of the disease.6
Glaucoma affects peripheral (side) vision and noticeable symptoms include tunnel vision, a narrowed field of view, coloured rings when looking at bright light sources, and a general loss of visual acuity and contrast perception. Sometimes it also causes parts of the visual field to disappear. It can affect one or both eyes, and if left untreated, can cause total vision loss.
It can be described as a silent disease, because even when vision is affected, the brain is designed to cope with changing circumstances and will complete this missing information, so the person affected remains unaware of the symptoms.
Glaucoma cannot be prevented, but if you manage the risk factors associated with the eye disease, blindness can be avoided.
If you’re at a higher risk for developing glaucoma due to ethnicity, diabetes, your family history or age, for example, it’s important to go for regular glaucoma screenings.
Individual lifestyle factors can also play a role. Your risk of developing glaucoma can effectively be reduced by keeping high blood pressure at bay, managing sleep apnea and monitoring cortisone treatment with the help of your healthcare practitioner.
Warning signs to look out for include:
- Chronic headaches
- Blurred vision
- Pain behind the eye
- Teary eyes
If you experience any one, or a combination of these symptoms, visit your nearest eye care professional or eye doctor and ask for a glaucoma test.
How often should you have your eye pressure checked?
What does a glaucoma screening involve?
This is the most common routine test done by eye care professionals to measure inner eye pressure. An instrument called a tonometer emits a small puff of air into the eye and measures its pressure. It’s not a painful or invasive test and it will only take a few minutes, but you may experience a little discomfort.
Using the tonometer readings, your eye care professional can then interpret the values. Although eye pressure is unique to each individual, according to the Glaucoma Research Foundation the range for normal pressure is generally between 12-22 mm Hg, but most glaucoma cases are diagnosed above 20 mm Hg.
Something to keep in mind here, is that a tonometry reading gives a rough indication of your eye pressure at a certain time. Similar to blood pressure, eye pressure can also vary between readings.
Your eye care professional will be able to provide you with exact information on how your tonometry values are interpreted, and if anything seems unusual, they should refer you to an eye doctor.
Funduscopy and fundus photographs
Eye drops are used to dilate the pupils, and then the eyes are examined with a device called a funduscope, or photographed using retinal imaging technology to magnify the optic nerve. If anything looks unusual, you may need to undergo further tests.
This may be done when your tonometry reading indicates high eye pressure; if you have a family history, or are at risk of glaucoma. An eye specialist may also do a funduscopy as part of a routine check.
Because glaucoma is such a complex disease with many causes and symptoms, your eye specialist may do a combination of comprehensive exams. Further specialised tests you may have to undergo include a field of vision test, retinal fundus imaging or Optical Coherence Tomography (OCT), and pachymetry to measure the thickness of the cornea.
Surgical methods include:
- Laser surgery – where a laser is used to open clogged parts of the trabecular meshwork.
- Minimal invasive glaucoma surgeries – surgeries done with small devices making micro cuts to bypass or open blocked canals. This type of surgery is quick with minimal complications and fast recovery.
- Cutting surgeries – where a cut is made to open the canal and lower pressure. This includes trabeculectomy, sclerectomy, and viscocanalostomy and canaloplasty. Consult your eye care specialist or eye doctor for more information.
- Tube surgery – where a tube is permanently placed in the eye to drain the aqueous humour and manage pressure.
In general, glaucoma chances of recovery after surgery can be good if all contributing factors are managed, but unfortunately damage to the optical nerve cannot be reversed.