What Causes Glaucoma?
Glaucoma is an eye disease that can cause irreversible damage to your sight. Alarmingly, 50% of people don’t even know they have it. Although it’s not as prevalent as conditions such as cataract, one in every 50 Australians will develop glaucoma. Around the world, over 70 million people are affected by this disease. Certain factors can increase your risk of developing glaucoma, such as older age, high short- or long-sightedness, and even taking certain medications. However, risk factors do not explain the underlying mechanisms of glaucoma. What causes glaucoma, and how can it be treated?
What Causes Glaucoma?
Glaucoma is a type of eye disease known as optic neuropathy. This means the optic nerve, which carries neural signals from the eyeball to the visual parts of your brain, becomes damaged. The majority of cases of glaucoma occur because the pressure inside the eyeball, known as the intraocular pressure, is too high. However, glaucoma can develop even with normal intraocular pressures, a subcategory known as normotension or low-tension glaucoma. Glaucoma treatment is always aimed at reducing the intraocular pressure in an effort to protect and preserve the optic nerve.
The intraocular pressure of your eye is dictated by the balance of production and drainage of aqueous humour. Aqueous humour is a fluid produced inside the eye; it’s not the same as the tears when your eyes water. Intraocular pressure can fluctuate throughout the day and can be affected by a number of factors, even by something like drinking alcohol. However, when the outflow of aqueous humour is too slow compared to its production, we get a consistent increase in pressure. If this pressure rise is sustained at too high a level, it can cause damage to the optic nerve. In essence, that is what causes glaucoma.
However, exactly what causes the imbalance in fluid production and drainage is not fully understood. In addition to this, what causes glaucoma to develop when intraocular pressures are still within a normal range is even less understood. There are a few scenarios that experts know can cause glaucoma:
- An accumulation and blockage of pigment cells or other debris in the drainage channels where aqueous humour flows out
- A narrowed drainage structure created between the transparent cornea and the coloured iris
- Trauma to the eye resulting in damage to the drainage channels
- Congenital malformation of the eyeball, resulting in a poorly developed drainage structure
Other hypotheses for the development of glaucoma, particularly normotension glaucoma, include issues with blood circulation or immunity and oxidative stress.
How Do I Know if I Have Glaucoma?
Although glaucoma treatment is often effective and readily available, the typical lack of obvious glaucoma symptoms can delay getting help. In the vast majority of cases, glaucoma symptoms are undetectable until more advanced stages of the disease.
The reason that glaucoma symptoms are so difficult to notice is that it usually presents with no pain or any outward signs that something is amiss.
In the late stages, you may realise that your peripheral vision is missing.
For example, you may be slower to notice a car turning toward you from the corner of your eye. As we tend to be less attuned to our peripheral sight, it’s only when this vision loss is more pronounced that we begin to notice.
There is one type of glaucoma that may present with acute symptoms. This is known as acute angle closure glaucoma and involves a sudden closing of the drainage structure. This results in a very high spike in intraocular pressure. Acute angle closure glaucoma symptoms include:
- A red eye
- Severe pain in the eye and head
- Nausea with or without vomiting
- Blurry sight in the affected eye and seeing haloes around lights
Acute angle closure is an ocular emergency and needs to be treated at an eye hospital immediately. This may involve surgery or a laser procedure.
However, around 90% of glaucoma cases in Australia are of a type known as primary open angle glaucoma, which does not present with symptoms. Instead, it progresses quietly, slowly and gradually, damaging the optic nerve and causing vision loss starting in your peripheral sight.
The best way to catch glaucoma early is to attend regular eye tests, either with your optometrist or ophthalmologist. Your eye care professional will conduct certain routine tests whether they suspect you have glaucoma or not. Tests specific for glaucoma include:
- Tonometry. This is the measurement of intraocular pressure.
- Fundoscopy. This is to directly visualise the optic nerve, assess its colour and shape, and look for any other features that might indicate optic neuropathy, such as haemorrhaging.
- Optical coherence tomography (OCT). The use of OCT imaging in eyecare is a relatively recent development but has been pivotal in the diagnosis and management of glaucoma. OCT imaging provides invaluable details about the optic nerve, such as highlighting any areas of thinning and potential damage to the retinal nerve fibre layer.
- Visual field testing (VFT). VFT can be used in a number of applications but is most commonly used to diagnose and monitor glaucoma. Small lights or flickering bars are presented to different parts of your visual field, and you are required to press a button when you see them.
Options for Glaucoma Treatment
Depending on your specific situation, your ophthalmologist may suggest one or more types of glaucoma treatment options. They can include:
- Eyedrop medications. These will typically need to be used one to three times a day, long-term.
- A laser procedure. Laser treatment may involve creating a small hole in your iris to improve aqueous fluid outflow, known as an iridotomy. Lasers may also be used to perform trabeculoplasty, which helps to remove debris clogging the eye’s drainage channels.
- Surgery. There are several different types of surgical procedures to treat glaucoma. All these operations aim to improve the drainage of fluid from the eyeball to lower the intraocular pressure.
Note: Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner.
References
What is Glaucoma?
The Pathophysiology and Treatment of Glaucoma.
Glaucoma.
https://www.mayoclinic.org/diseases-conditions/glaucoma/symptoms-causes/syc-20372839
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