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Glaucoma – what you need to know

Glaucoma is the main cause of preventable sight loss in the UK.  Many of our clients tell us they have vaguely heard of glaucoma but don’t really know what it is, and a lot think they’re not at risk because they don’t have a family history of it or they aren’t diabetic.

The truth is that we’re all at risk but fortunately, with early detection through regular eye examinations, it can be picked up and treated in the very early stages.  With modern eye examinations and technology such as our OCT retinal scanner, it can often be picked up before any significant loss of vision has occurred!  If left undetected, glaucoma can damage almost half of someone’s useful field of vision before they become aware that anything is wrong; and once the sight is damaged it is impossible to restore.  You can see why we think it’s really important for people to be aware of glaucoma and make sure they’re getting checked!

What is it?  Glaucoma is a disease which causes gradual, progressive damage to the optic nerve.  The optic nerve transmits all the information gathered by the retina (the sensitive nerve layer inside the eye) to the brain, so any damage to the optic nerve means that part of the picture doesn’t get ’seen’.  Glaucoma is known to damage certain areas of the vision first, usually causing peripheral vision loss which can (if left untreated) cause tunnel vision and eventually blindness.  This process generally takes years and most people only become aware that something is wrong when about 40-50% of the nerve fibres have been permanently damaged.

What causes it?  Medical science still hasn’t fully answered this, unfortunately.  It was thought for many years that glaucoma was caused by high pressure in the eyes; we now know that although high pressure increases the risk of developing glaucoma, it is not the only factor.  Some people with high pressure never show any other signs of the disease, and some people with normal eye pressure have been found to have it.  Managing the pressure in the eye is still the ‘gold standard’ treatment and has been found to be very effective at preventing the disease from progressing, however we think there are probably other causes of glaucoma.

We know people who have a close relative with the disease are more likely to develop it, and certain ethnic groups are more at risk, so there is some genetic risk.  There has been some evidence to suggest that low blood pressure, and certain chemical markers in the blood might contribute too.  On the other hand it has been suggested that people who wear tight neckties or play wind instruments may be more at risk through temporary raised pressure in the blood vessels!

Whilst we still don’t fully know what causes it, fortunately methods of detecting glaucoma are now very advanced and treatment to lower the pressure in the eye is generally very effective for preventing vision loss.

Who is most at risk?  We know that certain people are more likely to get glaucoma, although there is no way of predicting exactly who it will affect.  The risk is higher for people:

  • over 40, or over 30 with an Afro-Caribbean ethnic background
  • with a sibling, parent or child affected by glaucoma
  • who are using steroid medication
  • with advanced diabetic eye disease

It is recommended that everyone has an eye examination every 2 years to screen for the disease, but those at particular risk would be advised to have an examination every year (your Optometrist will advise you how frequently you should be tested).  The NHS recognises that a family history of glaucoma is a well-known risk factor so they provide a free eye examination every year for anybody over 40 who has had a close relative with the disease.  Eye examinations are also free for diabetics and the over 60s.

How does an eye examination detect glaucoma?  There are signs of glaucoma that your Optometrist can recognise long before you would be aware of any problem with your sight.  Generally an Optometrist may use 3 main methods of looking for glaucoma; we are also very fortunate to have been able to invest in an OCT retinal scanner which can help pick up signs of glaucoma in the retina even earlier than we would have previously been able to detect it.  Your Optometrist will select which tests are appropriate when they examine your eyes.  More about the OCT later; the 3 usual tests still provide very valuable information and are described here:

  • Pressure test: measuring the eye pressure or ‘intraocular pressure’ tells us basically whether you have a normal fluid pressure in the eye.  The internal eye is constantly producing and draining fluid (completely separate from tear fluid or blood pressure), as some pressure is needed in the eye to help keep its shape.  Sometimes the eye can start to produce too much fluid, or the drainage channels can become blocked, leading to raised pressure.  It is known that steroid medication can raise the pressure in some people so it is particuarly important to have the pressure checked if you are taking any.  If the pressure in the eye gets extremely high it can cause severe pain and acute glaucoma, but often the pressure can be quite high with no outward symptoms.
  • Examination of the optic nerve head: we look at the optic nerve by looking into the eye with an Ophthalmoscope (a special torch), to make sure it is a healthy colour and shape.  Changes over time or a difference between the two nerves can lead us to suspect damage due to glaucoma, or other eye conditions.
  • Visual field: this tests the peripheral vision to see whether it is normal, or whether the eye is less sensitive in certain areas than would be expected.  We look for certain patterns of vision loss in glaucoma, and the visual field test can pick up very subtle vision defects that you would usually be completely unaware of.

OCT and glaucoma detection  The OCT scanner has proven a great leap forward in glaucoma detection.  Previously we had to rely on simply looking at the optic nerves to see whether they looked damaged, and trying to compare the appearance from visit to visit.  The OCT actually scans the thickness of the retinal tissue around the optic nerve to tell us whether it is normal compared to everyone else of the same age and ethnic background.  In addition to this it takes a scan of the centre of the back of the eye, the macula, which has now been shown to be one of the first areas to lose some retinal nerve tissue in many cases of glaucoma.  These two scans can help us pick up extremely subtle defects and changes in the health of the nerve often before we would detect them on the surface.   What’s more, the OCT can analyse change in the eye from one visit to the next, so it really does help us detect very subtle deterioration which may not normally be found.

We still use the other 3 tests alongside OCT as appropriate, as they each provide useful information about the general health of the eye and help build a picture of the likelihood of glaucoma.  OCT has just made it much easier to detect subtle changes and abnormalities early on, and helps us distinguish what’s normal from what’s not!  It is highly recommended for those at greater risk of glaucoma, but is a very valuable test for everyone to have.

So what happens if the Optician suspects I have glaucoma?  If you have signs of glaucoma or ocular hypertension (raised eye pressure), your Optometrist will refer you to see a glaucoma specialist (Ophthalmologist).  We may need to see you for repeat tests before arranging a referral, to make sure we really need to send you!  Very often, pressure readings can be high on one occasion and acceptable on the next, as eye pressure can vary for many reasons (including anxiety, and the time of day).

If you are referred, the specialist will examine your eyes to decide whether to treat you for glaucoma/high pressure; whether to monitor you for any change (which sometimes happens if they aren’t certain you need treatment); or whether to discharge you if they feel you aren’t at risk of glaucoma at that time.

If treatment is required, this usually involves using eye drops daily which help to lower the pressure in the eye.  This has been found to be very effective in preventing sight from deteriorating.  The specialist will want to monitor you regularly to ensure the treatment is still working and the glaucoma is not progressing.

If a diagnosis of glaucoma is confirmed, you need to advise DVLA of the diagnosis (as a condition of your UK license).  They then arrange for you to have a special DVLA version of the visual field test, testing both eyes together, to ensure you have adequate peripheral vision whilst driving.

We hope that this article has given you some useful background information on glaucoma.  It is not intended as a definitive guide to the condition as glaucoma detection and management can be very different from person to person.  If you have any questions or suggestions please contact us.  You should ensure you have regular eye examinations and your Optometrist will be able to provide unique advice based on your individual circumstances.

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