Glaucoma is an eye disease characterised by progressive damage to the optic nerve of the eye. It can occur in just one eye and not the other, or be present in both eyes but more advanced in one compared to the other. The optic nerve is responsible for carrying the signals received by the sensory cells of the retina at the back of the eye to the visual processing centres of the brain. Glaucoma is actually quite common – around 2 out of every 100 Australians have the disease. So, what is glaucoma and how is it treated? And are there any early signs of glaucoma you can look out for?
What is Glaucoma
Glaucoma is one condition in a category of eye diseases known as optic neuropathies. As mentioned earlier, glaucoma is diagnosed when the optic nerve is found to suffer progressive damage and loss of retinal nerve fibres. While the exact underlying causes of glaucoma are still yet to be fully understood, we know that at a basic level, optic nerve damage in this disease occurs because the pressure inside the eye, called the intraocular pressure, is too high for the health of the nerve. Typically, the normal intraocular pressure range is quoted as 10-21mmHg (millimetres of mercury), however, we can often find that people with pressures within this range still experience glaucoma, while a person with an intraocular pressure slightly over 21mmHg can still demonstrate a healthy, robust optic nerve with no signs of damage.
The intraocular pressure of the eye is determined by the balance of fluid production versus fluid drainage inside the eyeball. This fluid is known as aqueous humour.
If the production of aqueous humour is excessive, or if its drainage from the eye is impeded or slowed in some way, it can result in elevated intraocular pressures. It is common and entirely normal for the pressures of the eye to be asymmetrical, within about 3mmHg of each other, and for pressures to fluctuate throughout the day. Controlling the intraocular pressures underlies all forms of glaucoma treatment.
Risk factors for developing glaucoma include:
- Older age
- Family history of glaucoma
- Short-sightedness (myopia)
- Sleep apnoea
The Signs of Glaucoma
Unfortunately, most glaucoma cases in their early to moderate stages present with no symptoms, lending this eye disease the nickname of “the sneak thief of sight”. Despite being such a relatively common condition, around 50% of Australians with glaucoma are actually unaware they have it.
The optic nerve and retina of the eye contain no pain receptors so there is no pain or discomfort directly due to damage of the nerve. A small subcategory of glaucoma known as acute angle closure glaucoma can present with some noticeable symptoms, such as a very painful, red eye with blurred vision. This occurs when the intraocular pressures suddenly escalate to very high levels. However, the majority of glaucoma cases fall under another subcategory called open angle glaucoma, which results in a slower, more insidious pressure rise.
Ultimately, untreated glaucoma results in permanent vision loss. This typically begins in our peripheral vision, which is another reason why most people are delayed in realising when something is amiss. Unlike our central vision, we are often less aware of subtle changes to sensitivity in our peripheral field of view. When it comes to glaucoma, by the time we begin to realise our peripheral vision has deteriorated, the disease is already likely in its advanced stages.
Because glaucoma progresses so slowly and subtly, it is important to maintain regular eye exams with an eyecare practitioner even when you feel nothing is wrong with your eyes or vision. This gives you the best chance of catching the disease in its early stages before any significant vision loss, allowing the optometrist or ophthalmologist to implement appropriate glaucoma treatment to slow or prevent further deterioration. An eye examination is able to detect any signs of glaucoma even if the condition is in its early stages, and will involve tests including:
- Tonometry – a measurement of your intraocular pressure; this may be taken multiple times to observe how your pressures may change over time
- Ophthalmoscopy – directly visualising the optic nerve to assess its features, such as colour, shape, and size
- Optical coherence tomography – a retinal scan that can take important measurements such as the thickness of the retinal nerve fibre layer to detect any areas of thinning and damage
- Perimetry – also known as visual field testing, this is an assessment of the sensitivity of your peripheral vision and is very useful for monitoring glaucoma progression and any associated vision loss
Modern glaucoma therapies are fortunately quite effective in most cases, and a lot of research is being devoted into developing new treatments, particularly in an area known as “minimally invasive glaucoma surgery”, or MIGS. There are currently no treatments that can restore the vision loss incurred from glaucoma, however, the aim of therapy is to slow or halt any further loss.
Treatment options include medicated eye drops, laser treatment, and surgery, all of which aim to reduce the intraocular pressures to a level that maintains the health of the optic nerve. Not all therapies will be suitable or effective for all patients, but your treating doctor will work with you to find one that is the most appropriate.
Note: Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner.