Good Hope Eye Clinic

Low Tension/Normal Pressure Glaucoma

David Kinshuck

What is glaucoma?

a blocked drain causes the eye pressure to rise and damage the optic nerve

In ordinary glaucoma the nerve is damaged by pressure from a build up of pressure inside the eye enlarge

Glaucoma is a condition in which the nerve at the back of the eye is damaged. If severe, it can cause blindness, but most people do keep good sight indefinitely. It is explained in more detail on the Glaucoma page, which should be read in addition to this page.

In ordinary glaucoma the nerve is damaged by an unusually high pressure in the eye. The high pressure stops the blood entering the tiny blood vessels in the part of the optic nerve that enters the eye. Animation

 

 

 

Low tension glaucoma

low tension glaucoma may be cuased by poor blood flow to the optic nerve

In low tension glaucoma not enough blood reaches the optic nerve (the tiny blood vessels supplying the optic nerve are shown in red). enlarge

 

 

In this type of glaucoma we believe not enough blood reaches the tiny arteries in the optic nerve. Blood from the heart flows towards the head, and then to the eye. Behind the eye the blood flows in a small artery, and just behind the eye the small blood artery enters the optic nerve itself.
Inside the nerve this small artery provides even smaller tiny branches that reach the tissues of the nerve. Without its blood supply, the nerve becomes damaged, and the sight will be reduced

In low tension glaucoma it is thought part of the problem may be too low a pressure in the blood supply to the nerve. This is rather like having a low water pressure in a house... not enough water comes out of the tap.  We do no know why this is, but only rarely does the nerve become badly damaged.

There may also be a fault with the blood vessel oxygen extraction process, so that not enough oxgygen reaches the nerve cells in the optic nerve. See optic nerve circulation animation.

 

How does the treatment work?

aqueous fluid produced in the eye drains out; blood flows into the optic nerve

Aqueous fluid (green) is made in the middle chamber of the eye (shown by the 'taps'), and drains out at the side of the front chamber. Blood from the heart originally enters the nerve (shown in red). enlarge  

Treatment is drops in most patients. The drops lower the pressure in the eye so more blood can flow in. Occasionally an operation is needed as below.

Normally, fluid (a little like water, called 'aqueous humour') is made in the middle chamber of the eye. It then flows through the pupil to the front chamber, and then out of the eye through small drainage channels. These channels are like a 'sieve' in the kitchen used to drain rice.

 

 

 

Eye drops

Eye drops containing drugs can 'switch the tap' off that makes the fluid (top half of eye opposite). Less fluid in the eye leads to a lower less pressure (like a tyre that is not pumped up as much). This allows more blood to enter the eye, and more blood flowing to supply the optic nerve. Alternateively, drops open up the drain  (trabecular meshwork) so more aqueous can drain out, and this also lowers the pressure. Both types of drops lower the pressure and this lets more blood flow in to supply the nerve.

 

An Operation

trabeculectomy...surgery is occasionally needed to lower eye pressure

A small hole is made at the top of the eye, under the eyelid, to let the fluid drain out of the eye. As a result, the eye becomes softer, and more blood can flow in. enlarge

Occasionally an operation may be necessary. As part of the operation a small hole is made to let more fluid out of the eye. Your ophthalmic surgeon will discuss the pros and cons of the operation if it is necessary.

 

 

 

 

 

 

 

 

 

How is the sight affected?

A common type of loss of vision in glaucoma
visual fields become progressively worse if the eye pressure is not low enough

At first the sight is normal,

 

then a small area of poor vision may develop.

This can extend, affecting much of of the sight,

or nearly all the sight.

At first the sight is normal, but it if the glaucoma is severe, the sight may get  progressively worse as below. You cannot 'feel' glaucoma, and usually would would not know there was anything wrong in the early stages. Case 1 for students.

Initial field defects, central or peripheral Eye 14.

 

How does the doctor or optometrist know you have low/normal tension glaucoma?

A healthy optic nerve

a cupped optic nerve...caused by high pressure/too much fluid in the eye

A cupped, or damaged, optic nerve
enlarge

Glaucoma is found by an ophthalmologist or optometrist by

  1. measuring the eye pressure (for this & other details about your examination see)
  2. looking into the eye at the optic nerve (the nerve can appear 'caved in' which we call 'cupped', as though it has been pressed on. See photo, and Case 1 for students
  3. testing the field of vision: you sit in a special machine with your head still. Lights flash, and you are asked to press the button if you see the light. If you cannot see the brighter lights, this shows on the computer print out rather like the drawing of the 'castle' above. Here is an online website that enables you to test you own visual field.
  4. examination of angles for narrow angle glaucoma

 

 

 

Visual fields

The sight is tested in the clinic for this type of patchy vision, by a visual field testSee a result. In this test, you have to put your head in a type of 'gold-fish bowl'. Lights are flashed on, and you have to press a button when you see the lights. The computer in the machine compares your result to that of a 'normal' person of your age, and prints out a serious of dots and black areas. The black areas are the area of damaged sight.

 

Can you become blind?

Only if you were very unlucky will your sight become very poor. Hardly anyone becomes blind in that they cannot see anything at all, and only occasionally will your sight become very bad. If an ophthalmic surgeon recommends the drops, you should use them (unless you get side effects). Often the drops can make all the difference between keeping your sight and loosing it. (The same applies to an operation if your ophthalmic surgeon advises you strongly you should have one).

Surprisingly, only two out of three patients recommended drops actually use them regularly. If a doctor has advised to use the drops and you choose not to, it is only fair to be honest and mention this to your doctor. For most people with this type of glaucoma it makes very little difference if you miss the drops now and again, so do not worry if you forget to use them now and again.

 

a disc haemorrhage

the optic nerve is examined for 'cupping' and haemorrhages enlarge (this patient is also diabetic )

Tests each visit

At each visit these results will be analysed

  1. eye pressure...measured most visits
  2. optic nerve appearance and cupping....measured most visits. Generally a haemorrhage indicates the eye pressure is slightly high for the eye. They take 3-6 months to disappear.
  3. visual fields..tested about yearly (see this excellent IGA article which shows you how to interpret your visual field test...it also discusses how often the test should be carried out)

What can you do to help?

See General health below. The main thing is to use drops if your doctor has advised you to.  A few people have low blood pressure at night; ask you general practitioner if this is likely. There are no tablets and there is no magic cure though. Strangely, people with this type of glaucoma are more likely to have migraine or poor circulation in their hands (doctors call this 'Raynauds'). A low blood pressure is helpful (Kim 2010). Low tension glaucoma is related to general health vascular problems (Leung 2010).

Your general health in glaucoma/intraocular hypertension

Remember that your general health and lifestyle have a major impact on glaucoma and your sight. BJO 12

  • Smoking does increase the eye pressure, and will make your glaucoma worse. It also increases the risk of retinal vein occlusion (which occur in glaucoma), macular degeneration, cataracts, stroke, and heart attacks. The exact risk is not known, but in some patients 20 cigarettes / day will increase loss of vision by 400%. Passive smoking 20 a day is equivalent to smoking 5 cigarettes a  day, and increase visual loss 100%.
  • Metabolic syndrome is strongly related intraocular pressure (Nature 2010). This is related to (as below) lack of exercise, high blood pressure, obesity and liver and kidney problems. Treatment of the metabolic syndrome will help lower eye pressure 0.8mmHg..
  • Exercise lowers the eye pressure, 'an hour a day (walking) will keep the doctor away', and half an hour will help a lot. See. Any exercise will do... eg walking, swimming, gardening.
  • High blood pressure will be harmful as this may, together with the glaucoma, cause a retinal vein occlusion. A blood pressure of 140 systolic or less, may be best, and may be lower the better as long as you feel well. See   But there are other views. We now know that eye pressure and blood pressure are related; the implication of this is that lowering blood pressure will help in the treatment of glaucoma. So keeping your blood pressure reasonably low is an important part of the treatment, although too much medication may cause problems.
  • Oily fish will help the circulation and probably help prevent retinal vein occlusions. Red meat  (including pork/ham) increase blood pressure; they are best replaced, at least in part, by fish, and pulses such as lentils and beans. Nuts have some healthy fats, and may be helpful in small amounts...but they are 'fattening' and help to put weight on.  A Mediterranean diet helps.
  • 9 portions of vegetables or fruit a day will also help to keep your retinal veins and macula healthy, and prevent cataract formation...9 a day (men) 7 (women) keeps the doctor away...
  • A high saturated fat diet is very harmful as it will contribute to many conditions. A balanced diet is recommended. Saturated fat comes from full-fat diary products such as milk, cheese, many cakes and biscuits, and red meat. Statins help (surely a benefit of a low cholesterol).
  • Salt will increase blood pressure.
  • binge drinking, eg 4 pints of beer in one day, or more that 3 glasses of wine/day, will cause a rise in blood pressure, again contributing to all these conditions. Coffee increases PXF glaucoma.
  • Obesity results in high blood pressure, lack of exercise, and indirectly will cause problems. Many obese patients suffer from sleep apnoea....
  • Sleep problems. New research links sleep apnoea with glaucoma. Sleep problems are very common in obesity...these are likely if you snore a lot. Logically if you are overweight, it is important to lose weight to help your glaucoma. So if you do snore a lot, do lose weight, and ask your doctor if you need to be tested for sleep apnoea. 2012 2014
  • Steroid medication puts eye pressure up. Even inhaled nasal steroids can increase the pressure 2.5mmHg. If you use nasal steroids (eg for allergic rhinitis), ask your doctor if you can reduce or stop them. Steroid tablets certainly may put eye pressure up; ask your doctor if you can reduce the dose (Do not reduce steroid tablets without seeking advice.).
  • Retinal vein occlusions: patients with glaucoma are much more prone to retinal vein occlusion. The risk of a vein occlusion is reduced by control of the glaucoma, blood pressure, and all the other general health risk factors immediately above.

CNS changes

There may be CNS changes in LTG. RCO 2011.

 

Leaflet download

a leaflet explaining low tension glaucoma

This web page/leaflet is designed to accompany the Glaucoma page  or Glaucoma leaflets available in an Eye Clinic; ask for one in your clinic if you have not seen one.

 

Notes for professionals

  1. Need careful history
  2. test colour vision
  3. check APD
  4. check disc pallour relates to field
  5. look for notch & nerve fibre layer defect and relationship to field
  6. patients should not notice defect..if patients notices defect, risk of neurological problem higher (I would add particularly observant patients may notice glaucoma defects.)
  7. hyper-homocyseinaemia (MTHFR gene) is linked to NTG
  8. CSF pressure may be relevant.
  9. vitamin B12 an folate tested needed in all patients, perhaps every 5 years