Glaucoma

Glaucoma is a group of diseases that damage the eye’s optic nerve and can result in vision loss and blindness. It is the second most common cause of blindness worldwide after cataracts. With early detection and treatment, severe vision loss can be prevented. It is for this reason that everyone over the age of 45 should see their optometrist for an eye check every 2 years and earlier if there is a family history.

Glaucoma is usually associated with an intraocular pressure (IOP) above the normal range. However:

• 20-50% of patients with glaucoma have IOP within the normal range. Patients with normal IOP are said to have normal tension glaucoma.
• Many patients have raised IOP for years without developing characteristic changes of glaucoma. This condition is referred to as ocular hypertension.

What are the symptoms of glaucoma?

Often glaucoma develops without any symptoms. There is commonly no pain and central vision often stays normal until late stages of the disease. Therefore it is important for patients with glaucoma to have regular specialised visual field tests to assess the amount of peripheral vision being affected.

Without treatment, people with glaucoma will gradually lose their peripheral vision. Over time, central vision may decrease until no vision remains. Glaucoma can develop in one or both eyes.

Glaucoma can be classified as open angle or close angle.

In angle-closure glaucoma, the drainage angle at the front of the eye is blocked by part of the iris and fluid cannot drain through the angle and leave the eye. This type of glaucoma is more common among Asian patients. People with this type of glaucoma may have a sudden increase in eye pressure. Symptoms include severe pain and nausea, as well as redness of the eye and blurred vision. If you have these symptoms, you need to seek treatment immediately. This is a medical emergency. Without treatment to restore the flow of fluid, the eye can become blind. A laser treatment called peripheral iridotomy to create a small channel on the iris near the angle can prevent this emergency from occurring.

In open-angle glaucoma, the drainage angle is not blocked by the iris. Open-angle glaucoma forms the majority of glaucoma in Australia. In open-angle glaucoma, even though the drainage angle is open, the fluid passes too slowly through the meshwork drain. This causes fluid build-up and the pressure inside the eye rises to a level that may damage the optic nerve. When the optic nerve is damaged from increased pressure, open-angle glaucoma and vision loss may result. There is no single value of eye pressure that will cause glaucoma. The damage to the optic nerve occurs when the balance between eye pressure and the optic nerve’s ability to handle pressure is lost.

• People with a family history of glaucoma
• Older age
• Patient with migraines or Raynaud’s (a condition that causes very cold fingers and feet) or low blood pressure especially at night.
• Some patients with obstructive sleep apnoea

For detection of glaucoma your eye specialist will perform a comprehensive eye examination to examine the eye pressure, drainage channels of your eye and optic nerves.

Additional tests you will have include:

• Visual field test: This test assesses your peripheral vision. It helps your eye care professional tell if you have lost peripheral vision, a sign of glaucoma.
• OCT (Optical Coherence Tomography) scan: This test assesses the amount of neural tissue present in your optic nerve and the population of neural cells (ganglion cells) in the retina. The OCT and visual field test forms an integral part of documenting the structure and functional changes caused by glaucoma. It is important for diagnosis of glaucoma as well as assessing whether there has been any progression.
• Optic nerve photography: This is a special photograph of the optic nerve to document its appearance for future reference.

The peripheral vision lost from glaucoma cannot be restored. There is no cure for glaucoma, however if the eye pressure (IOP) is lowered to a safe level then glaucoma will not progress.

What is a safe eye pressure for you may be different to other people. Many factors need to be taken into consideration including your age and the degree of existing glaucoma damage. Your eye specialist will advise you on the eye pressure that is safe for your eye (known as the target eye pressure).

The aim of these treatments is to prevent progression of your glaucoma by achieving a pressure that is safe for the eye.

• Eye drops – These are the most common form of treatment for glaucoma. Patients will need to use these on a daily basis and therefore compliance is important.
• Selective Laser Trabeculoplasty (SLT) – SLT is a non-invasive laser procedure that treats the drainage channels in the eye to encourage greater fluid flow. It can be in addition to, or instead of eye drops.
• Minimally Invasive Glaucoma surgery (MIGS) – MIGS involves various micro devices to allow fluid drainage out of the eye with less trauma and post-operative complications than conventional surgery. The long-term effectiveness of these procedures is not clear.
• Conventional surgery (Trabeculectomy or Tube shunt operation) – These are drainage procedures performed when medical, laser therapy or MIGS have failed. The long-term effectiveness of these procedures are well established however post-operative complications are significant.
• Cyclodiode laser – Cyclodiode laser treatment is commonly used in intractable glaucoma or eyes with poor vision.