Many people have heard of glaucoma before but aren’t quite sure what it is. Some confuse it with cataracts, while others assume it’s a normal and inevitable part of ageing. Neither is quite accurate. So, what is glaucoma, and how is it diagnosed and managed? Keep reading to find out.
What is Glaucoma?
Glaucoma is a type of eye disease affecting about 300,000 Australians. Along with a few other conditions, it’s part of a group of diseases known as optic neuropathies. This refers to disease and damage of the optic nerve at the back of the eyeball. The optic nerve is responsible for transmitting neural signals from the eyeball itself to the brain, which is then converted into our perception of sight. Without a functioning optic nerve, we lose vision.
Someone developing glaucoma experiences progressive damage to their optic nerve. The entire nerve doesn’t lose its function all at once, though if glaucoma treatment is delayed, then a significant portion of the nerve fibres can be lost. As the fibres become damaged, the area of your field of view served by those fibres loses its sensitivity. This means that you begin to lose vision in that part of the retina. When developing glaucoma, this loss of your visual field typically begins in the periphery. Because we’re less attentive to our peripheral sight, patients tend not to be aware of any changes until glaucoma has progressed significantly.
There are two broad classifications of glaucoma: open-angle and closed-angle glaucoma. The anterior angle is the anatomical structure created by the coloured iris and the clear cornea. The majority of aqueous fluid produced within the eyeball drains out through this structure. As the names suggest, open-angle glaucoma occurs in the presence of this drainage channel being wide open. In contrast, in closed-angle glaucoma, the space between the iris and cornea is narrowed, which physically impedes the outflow of aqueous fluid.
Most cases of glaucoma occur from raised pressure inside the eyeball, known as intraocular pressure. In open-angle glaucoma, something is either inhibiting the outflow of aqueous or stimulating excessive production. This imbalance of aqueous production and outflow is what can raise intraocular pressure. The elevated pressure damages the optic nerve, leading to glaucoma. However, there is a subset of glaucoma known as normotension or low-tension glaucoma. This is when damage and deterioration of the optic nerve progress even though the intraocular pressure is within a normal range.
There are typically no symptoms of glaucoma until it’s too late and a significant amount of sight has been lost. However, in acute closed-angle glaucoma, the intraocular pressure may spike very high and very suddenly. This can lead to symptoms including:
- Red eye
- Headache or eye pain
- Blurry vision and haloes around lights
Acute angle closure is an ocular emergency that needs glaucoma treatment immediately to prevent profound sight loss.
What is Glaucoma Testing?
As mentioned above, it’s almost impossible to tell you’re developing glaucoma by trying to look for symptoms. Instead, most cases of glaucoma are caught on a routine eye exam with an optometrist or ophthalmologist.
During a regular eye check, your eyecare professional will perform certain tests that can help to identify a risk of glaucoma. Not one test is considered to be diagnostic of glaucoma; your clinician needs a series of results that concur and demonstrate progressive optic nerve damage. These tests include:
- Tonometry. Measuring an intraocular pressure that is borderline or above the normal range will alert your eye care professional to conduct further tests for glaucoma diagnosis.
- Fundoscopy. In ophthalmology, the fundus refers to the retina. Fundoscopy is simply viewing the retina, which just requires a light source and magnification system. This allows your clinician to assess the optic nerve for colour, size, and any irregularities of the neuroretinal rim.
- Retinal photography. Taking a photo of the retina can help to record the appearance of the optic nerve for future comparison.
- Optical coherence tomography (OCT). OCT scans are now considered to be crucial for the diagnosis of glaucoma and the monitoring of progression. An OCT machine can measure the thickness of the retinal nerve fibre layer to detect any damage and thinning.
- Gonioscopy. Gonioscopy is often not performed routinely, but if there is a suspicion of glaucoma, your eye care professional may perform this test to view the anterior angle. This can assess how open the angle is and whether there is any pigment or debris blocking the drainage channels.
- Visual field testing (VFT). VFT is not a routine test for a normal eye check but is done frequently if glaucoma is a concern. This test measures the sensitivity of your visual field and can detect areas of sight loss from optic nerve damage due to developing glaucoma.
What is Glaucoma Treatment?
The aim of glaucoma treatment is to lower the intraocular pressure in an effort to protect the optic nerve. This is applicable even in normotension glaucoma when the intraocular pressure is already considered within the normal range. In addition to managing intraocular pressure, there is some evidence that vitamin B3 may be protective of the optic nerve.
First-line glaucoma treatment is often in the form of medicated eye drops. This is a class of medications that lower intraocular pressure, including beta-blockers and prostaglandins. Some ophthalmologists may suggest a laser treatment as the first option. The most common is known as selective laser trabeculoplasty, which uses a laser to help clear the anterior angle for better fluid outflow. For more stubborn cases of glaucoma, surgery is also an option, such as inserting shunts or tubes to aid aqueous drainage.
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Note: Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner.
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