What is Glaucoma?

What is glaucoma?

  • Glaucoma is the name given to eye conditions in which damage occurs to the optic nerve related to the pressure inside the eye.
  • This usually begins as loss of the outer part (periphery) of vision and, if left untreated, can progress to tunnel vision and eventually loss of central vision.
  • Once vision is lost it cannot be recovered.
  • With early detection and treatment, most people have good vision for life.

How is the eye affected by glaucoma?


Glaucoma occurs when the pressure in the eye (intraocular pressure, IOP) is too high for the nerve of sight to remain healthy. Exactly how pressure damages the nerve is not completely understood.

The normal range of eye pressure is 6-21. However, some people are more sensitive to pressure than others. For some, typical glaucoma damage occurs at a relatively low eye pressure; for others the pressure can be quite high and yet no damage is done – this is called ocular hypertension.

Where the eye pressure does rise above normal, this is usually because the drainage of fluid out of the eye is reduced and too much fluid builds up inside the eye. As the nerve starts to be affected, nerve fibres start to die off in the rim of the optic disc.

Glaucoma is one of the leading causes of preventable blindness.It affects two per cent of people over the age of 40, and this rises to five per cent of people over the age of 80.


Risks Factors for the development of Glaucoma

Family history of glaucoma;

  • There is at least a four times increased risk of developing glaucoma if you have a close blood relative with the condition (father, mother, brother, sister, or child).
  • People with close relatives should get tested by their optician so, if you have glaucoma, don’t forget to tell your relatives about the condition and the need for them to be tested.

Genetic Links

There are more than 200 genes associated with an increased risk of glaucoma so inheritance isn’t clearcut. Research ism ongoing searching for genetic markers of high risk or aggressive disease.

Blood pressure

People with very low blood pressure have a greater risk of worsening of glaucomatous sight loss.


  • People of African-Caribbean origin have about a four times increased risk of POAG when compared with those of a European origin and the condition also tends to come on at an earlier age and be more severe.
  • People of Asian origin are at an increased risk of developing angle closure glaucoma.

Glasses prescriptions

  • People with short sight (myopia) are at increased risk of developing glaucoma.
  • Long sighted (hypermetropia) people are known to be at increased risk of developing angle closure.


People with diabetes are at increased risk of developing glaucoma, although it is not known whether there is a direct link between the two conditions.


The prevalence of glaucoma increases with age.

 How is glaucoma identified?

Glaucoma has no obvious symptoms in the early stages. It is usually painless and vision loss occurs slowly and unnoticed until it is quite advanced. Although patches of vision are lost, they are off centre and often, at first, one eye can fill in the gaps for the other eye. If it is not treated it can eventually lead to severe or even total loss of vision. But, if found and treated early, the outlook is very good. For most people, glaucoma is picked up by their optician (optometrist) at a routine sight test.

There are three main tests:

  1. Looking at the appearance of the optic nerve in the eye (the optic disc), checking for cupping. This can be done by looking at the eye with a special torch (ophthalmoscope), on the slit lamp (specialist eye examination microscope), by eye photographs or by scans of the eye (OCT, HRT).
  2. Measuring the pressure in the eye (tonometry). This is ideally done on the slit lamp as this is the most accurate method, but it can also be done with other instruments including a puff of air or a hand held instrument.
  3. Checking the field of vision (visual field test, perimetry). This maps out any blank or weak spots in the vision including at the edge of your vision.

Other important tests for people who have or are suspected to have glaucoma include:

Central corneal thickness – thick corneas can cause the pressure to seem artificially high and it helps interpret the significance of a high or low pressure.

Gonioscopy; looking at the drainage area inside the eye with a special lens.

Some people have an optic disc cup shape that looks similar to early change in glaucoma but without any changes in the visual field. This optic disc appearance can be normal for them, as the optic nerve shape varies in different people.