What is Glaucoma?
The paradox is that there is no disease called "Glaucoma" ........ but there is a family of diseases called "The Glaucomas". There are about 12 different sorts of glaucoma, some of which are exceedingly rare. The management of glaucoma is a medical prerogative, and opticians cannot manage glaucoma except on what is called a "shared care" basis. What all the glaucomas have in common is that they damage vision by damaging the optic nerve that carries data from the eye to the brain. It must be remembered that all glaucomas are serious and have the potential to cause blindness.
One of the commonest is "Primary Open Angle Glaucoma" or "Chronic Open Angle Glaucoma". This disease has no symptoms – you don't know you have it – until you have lost almost all your vision and start bumping into things. The tragedy is that blindness from glaucoma is preventable; if the diagnosis is made early, then drugs given as eye drops are highly successful. Some people cannot believe that they would not notice that they are losing their vision, but since the loss of vision in this type of glaucoma is in the periphery of the visual field, it really is true that unless some-one finds it for you, you won't know you've got it! If you are over 40 you should have an eye test every 3 years and over 50 every 2 years to screen for glaucoma. You are particularly at risk if you have a relative with glaucoma. Although this type of glaucoma is often associated with high eye pressure, in many cases the pressure is normal, so just doing a pressure test is inadequate to make the diagnosis.
If you're not happy with the screening by an optometrist, you should see a medically qualified Consultant Ophthalmologist.
In many cases, there are none until there is advanced loss of vision which is why it is such a dangerous condition.
In general treatment is medical with powerful drugs given as eye drops. Sometimes, laser treatment may be indicated, and more rarely conventional surgery. It is important to have an exact and accurate diagnosis to plan logical treatment, and this can only be done after an examination by a Consultant Ophthalmologist. Special tests such as gonioscopy, pachymetry, tonometry and field analysis are likely to be required. Gonioscopy is examination of the drainage angle of the eye: the drainage angle is a "sieve" where the aqueous fluid goes out of the eye. Inspection requires the use of a diagnostic contact lens which is placed on the eye momentarily. This is required to define whether the glaucoma is "open angle" or "closed angle" – a fundamental sub-division. Pachymetry is measurement of the thickness of the cornea, usually with an ultrasound device. This is important as pressure readings are falsely high if you have a thicker than average cornea, but more dangerously falsely low if you have a thin cornea, either naturally or after laser vision correction. Tonometry is the measurement of the intraocular pressure (IOP) using a Goldmann Tonometer: the "gold standard". This works by the Imbert-Fick principle, and the reading needs to be corrected for the thickness of the cornea as measured by pachymetry. Nevertheless, you should know that a normal IOP does not mean you don't have glaucoma: you need a full examination by a medically-qualified ophthalmologist. Field testing is required to see if there is any damage to the visual field. This is done separately for each eye and you will be asked to "click" whenever you see a light flash in the periphery of your vision. Modern field analysers are highly sophisticated and will "try" to catch you out, for example sometimes clicking and flashing, sometimes flashing only and sometimes clicking only, so you need to understand that this is a "performance" test and come in the right frame of mind to "perform" – easier said than done perhaps! Nevertheless, if you have glaucoma you will need field testing at least once a year.