Courtesy of David Kinshuck © Good Hope Hospital
Glaucoma is usually caused by too much fluid pressing on the nerve at the back of the eye. There are many types of glaucoma, but on this page glaucoma is the term given to the ‘chronic open angle’ or ‘primary open angle’ or ‘chronic simple’ glaucoma.
Pseudoexfoliation and pigmentary glaucomas are both chronic open angle glaucomas, and this page applies.
Glaucoma is not a single disease, but represents conditions that occur for different reasons with the final event being optic nerve damage and visual field loss
Types of glaucoma
- chronic open angle(this page)
- narrow angle
- angle dysgenesis
|The eye is a round ball the size of a small tomato.|
|It is partly hidden behind the eyelids.|
|Imagine the eye turning as shown below…|
then imagine ‘cutting’ through the eye ball…
|…..this is the view used below to explain glaucoma.The green arrow shows the flow of fluid, like water, through the eye.|
The optic nerve in glaucoma
The optic nerve is the ‘electric wire’ of the eye, an it takes messages about what you see on towards the brain. In the main type of glaucoma the optic nerve is pressed on by extra fluid in the eye, and this may damage the sight in the eye.
Everybody’s eye produces a fluid like water in its middle chamber. This fluid then flows around inside the eye to the front chamber, as shown in the diagram below… the blue arrow.
Normally fluid is made in the ciliary body and circulates to the front chamber, where it drains through the trabecular meshwork out of the eye.
Then, from the front chamber the fluid leaves the eye by entering a drainage meshwork, like the drainpipe of a sink or bath. From this drainage system the fluid enters the bloodstream. The trabecular meshwork is a type of filter system.
In the common type of glaucoma this drainage system can block. The fluid gets trapped in the eye, and the pressure inside the eye goes up like a tyre being blown up to much.
This pressure or fluid then presses on the nerve at the back of the eye. If the pressure is high or continues for a long time, usually years, the nerve at the back of the eye may become damaged, and eventually the sight may be affected.
The pressure reduces the blood flow in the tiny blood vessels in the optic nerve.
Intraocular presure is strongly related to the metabolic syndrome. Metabolic syndrome and other insulin resistance-related features, including hepatic steatosis, increased left ventricular mass, and proteinuria, are strongly associated with IOP.
|The eye produces its own fluid, like a ‘tap in the bathroom’, in its middle chamber.The fluid …like water.. flows through from the middle to the front chamber, the eye. The fluid then drains out of the eye through a ‘drain’, like the plughole of a sink (the trabecular meshwork).||If the drain blocks, the fluid cannot get out of the eye, and the pressure in the eye builds up like a car tyre being pumped up too much.This pressure damages the optic nerve at the back of the eye, pressing it in.|
Glaucoma is much commoner as we get older but tends to run in families.
Genes control the blockage of the drain (the ‘trabecular meshwork’). The relations of patients with glaucoma should all be checked for the condition. If you have glaucoma and you are 70y, then all the relations (mainly children and sisters and brothers) should be checked from the age of 50y. If you have glaucoma age 30y, then even the children related to you should be checked (again: sons/daughters/brothers/sisters).
There are 3 particular genes (open angle glaucoma).
These influence the drainage of aqueous humour through the trabecular meshwork. For instance, and abnormal protein may be produced, and this becomes trapped in the trabecular meshwork cells, and is toxic.
These influence the axons in the optic nerve in low tension glaucoma. The retinal ganglion cells are weaker than usual and die earlier.
There are many other genes: some affect the optic nerve, others affect the trabecular meshwork cells (transport across membranes. Others are related to blood fat levels (toxic to the optic nerve).
There be be visual field defects that may be glaucoma related.
At first the sight is normal, but it if the glaucoma is severe, the sight may get progressively worse as opposite.
then a small area of poor vision may develop.
This can extend, affecting much of of the sight,
or nearly all the sight.
A common type of loss of vision in glaucoma.
How does the doctor or optometrist know you have glaucoma?
Glaucoma is found by an ophthalmologist or optometrist by
- measuring the eye pressure (for this & other details about your examination
- 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.
- 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.
Chronic glaucoma is treated with
- eye drops…95% patients
- laser helps a few patients
- some patients need surgery
Will the sight get worse?
Once the pressure reaches a satisfactory level the glaucoma should not
A satisfactory pressure if the optic nerve is healthy is 18-20mmHg, if the nerve is slightly damaged 14-16, and if considerably damaged 10-12 would be ideal.
(The pressure level needed also depends on your type of glaucoma. People with ‘low tension glaucoma’ need a lower pressure, for instance.) People who have a pressure of 14 that never rises above 14 usually notice little progression.
Effectively research has shown that if a pressure is 10mmHg, hardly any eye will be further damaged from pressure, if 11mmHg, then 10% of eyes/patients will notice a deterioration, and so on up to 20mmHg.
It is very hard for an ophthalmologist to tell which eyes will get worse, but
- eyes with healthy looking optic nerves can take a higher pressure
- anaemia, migraine, cold hands, sleep apnoea, suggest a lower pressure is helpful
- if the visual field is full, a higher pressure may be well tolerated
- younger patients with very cupped discs and visual field missing do need very low pressures, ideally 10mmHg
- people with optic disc haemorrhages are at much higher risk
At 20mmHg most eyes will deteriorate. But in practice the risks of treatment, such as having to use lots of drops, and particularly that of diamox tablets or surgery, have to be balanced against the ideal of seeking a pressure of 10 for all patients. In practice accepting a higher pressure in a particular patient may still mean very few patients notice much deterioration, and is the best option. Indeed, in an elderly patient using 2 or 3 drops there may be no safe alternative, especially if this includes xalatan (or lumigan or travaprost).
Tests each visit
At each visit these results will be analysed
- eye pressure…measured most visits
- optic nerve appearance and cupping….measured most visits
- visual fields..tested about yearly
New equipment can help make the diagnosis, but such tests are often inconclusive. This scan shows ‘suspicious’ discs, the patient may have glaucoma (‘glaucoma suspect’: visual fields were full and pressures normal). Glacuoma is more likely to be present if the comp[uter measures a thinnner nerve fibre layers, as indicated in red (the circles surrounding the optic disc, white arrow, 0.7 cupping right and left).
Remember that your general health and lifestyle have a major impact on glaucoma and your sight.
- 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 ciagettes / 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 sydrome is strongly related intraocular pressure. 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. 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. 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 reaonably low is an important part of the treatment, although too much medication may cause problems.
- Obesity results in high blood pressure, lack of exercise, and indirectly will cause problems. Many obese patients suffer from sleep apnoea….
- Oily fish will help the circulation and probably help prevent retinal vien 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.
- 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.
- Salt will increase blood pressure.
- binge drinking, e.g. 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.
- Sleep problems. New research links sleep apneoa 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.
- Steroid medication puts eye pressure up. Even inhaled nasal steroids can increase the pressure 2.5mmHg. If you use nasal steroids (eg for allregic 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.