What is glaucoma?


What is it?

Glaucoma can affect sight, usually due to a build-up of pressure within the eye or the eye being more prone to damage from pressure. Glaucoma is a group of eye diseases that affect the optic nerve, which connects the eye to the brain. It often affects both eyes, usually to varying degrees. One eye may develop glaucoma quicker than the other.

Types of glaucoma

There are various types of glaucoma including:

  • Chronic (open-angle) glaucoma – this is the most common type of glaucoma and develops very slowly.
  • Acute (angle-closure) glaucoma – this is rare and may develop rapidly with a sudden, painful build-up of pressure in the eye. Other symptoms may include blurred vision and haloes around lights.
  • Low-tension or normal tension glaucoma. Occasionally optic nerve damage can occur in people with so-called normal eye pressure. This form of glaucoma is treated in the same manner as open-angle glaucoma.
  • Secondary glaucomas. These glaucomas can develop as a result of other disorders of the eye such as injuries, cataracts, eye inflammation. The use of steroids (cortisone) has a tendency to raise eye pressure and therefore pressures should be checked frequently when steroids are used.

How common is it?

  • About 91,000 New Zealanders (2% of the population') over the age of 40 have glaucoma and more than half don’t know they have it. That means there is a very real possibility they will go completely blind.
  • Worldwide 4.5% of the population over 40 years old has glaucoma ‒ 64 million people ‒ and that’s expected to grow to 111.8 million worldwide by 2040.

Source: Ophthalmology. 2014 Nov;121(11):2081-90. doi: 10.1016/j.ophtha.2014.05.013. Epub 2014 Jun 26.

Risk factors for glaucoma include:

  • A family history of the disease
  • Higher levels of short sightedness
  • Raised pressure in the eye which is called ocular hypertension (OHT)
You are also at increased risk of developing chronic glaucoma if you are of black-African or black-Caribbean origin. Acute glaucomas are much less common. However, people of Asian origin are more at risk of getting this type of glaucoma compared with those from other ethnic groups.

Glaucoma In families

Having a family history of glaucoma puts someone at greater risk of developing glaucoma themselves. Direct family members (parents, siblings and children) of a person with glaucoma have an almost 1 in 4 chance of developing glaucoma in their lifetime.

  • Have a family history of glaucoma
  • Are over the age of 40
  • Have diabetes or migraines
  • Are short or long sighted
  • Take cortisone drugs (steroids)
  • Have had eye surgery or an eye injury

Source: https://www.glaucoma.org.au/about-glaucoma/who-is-at-risk

What causes it?

The eyeball contains a fluid called aqueous humour which is constantly produced by the eye, with any excess drained though tubes. When the fluid cannot drain properly, this causes a build-up of pressure in the eye known as the intraocular pressure.

Glaucoma develops when this increased pressure damages the optic nerve (which connects the eye to the brain) and the nerve fibres from the retina (the light-sensitive nerve tissue that lines the back of the eye).

In acute glaucoma cases this pressure rises rapidly to higher levels, causing pain.

Vascular dysfunction has also been shown to exist in patients with normal-tension glaucoma.

Diagnosing glaucoma

Glaucoma can be treated but early detection is important. If left untreated, glaucoma can cause visual impairment and damage that cannot be reversed. But if it's detected and treated early enough, further damage to vision can be minimised or prevented.

If you have chronic glaucoma, it can take a long time before you realise you have a problem with your eyesight. This is because chronic glaucoma is painless and usually damages the outer edge of the vision and works slowly inwards. Without regular eye tests you may not notice a problem until the glaucoma is near the centre of your vision.

1Glaucoma is the Slight Thief of Sight - RANZCO recommends "have your optic nerves checked every 2 years"

It is recommended that people have a regular optic nerve check from age 50 and from age 40 for those of African or Asian descent. Those with a positive family history should be checked from age 35 as they have a significantly increased risk. Most people are recommended to have an eye check for glaucoma every 2-3 years or when advised by their eye health professional.

Acute glaucoma is rare but usually painful often accompanied by blurred vision and haloes around lights. If you get these symptoms it is important to seek immediate assistance. Contact your optometrist, general practitioner or local Accident and Emergency department on 000. Even if the symptoms go away you should contact your optometrist as soon as possible as repeat episodes can cause damage to your eyesight.

Source: 1 https://ranzco.edu/media-and-advocacy/blog/fast-facts-about-glaucoma

Tests for glaucoma

There are several tests that can be carried out by your Specsavers optometrist in addition to the usual examinations carried out during an eye test. They are painless and quite quick. They include:

Eye pressure test (tonometry)

An instrument called a tonometer is used to measure the pressure inside your eye – intraocular pressure. Tonometry can be useful to identify ocular hypertension (OHT – raised pressure in the eye), which is a risk factor for chronic open-angle glaucoma.

Visual field test

You will be shown a sequence of light spots and asked which ones you can see. Some dots will appear in your peripheral vision, which is where glaucoma begins. If you can't see the spots in your peripheral vision, it may indicate that glaucoma has damaged your vision.

Optic nerve assessment

Your optic nerve connects your eye to your brain. This can be assessed in a variety of ways during your examination and it is also photographed using a retinal camera. Digital retinal photography (DRP) captures an image of your optic nerves which can be used as reference for future visits and to track any changes that may occur over time.

Managing glaucoma

If your Specsavers optometrist suspects glaucoma, you will be referred to an ophthalmologist for further tests. If the ophthalmologist confirms a diagnosis of glaucoma, they will also be able to explain:

  • How far the condition has developed
  • How much damage the glaucoma has done to your eyes
  • What may have caused the glaucoma

They will then be able to advise on treatment which in most cases is simply an eye drop used on a daily basis coupled with regular follow-up appointments.

Drops may be used to examine your eyes in a glaucoma appointment – these can temporarily affect your vision. Please check when making the appointment if you will be able to drive immediately after the appointment.