- Posted by Admin on January 25, 2010
Hey Everyone,
Last time I blogged I told you about glaucoma. I realised that I mentioned some tests without really explaining what they were, so that's what I'm going to try to do today.
Intraocular pressure
This is the pressure inside your eye. There is a fluid that nourishes the eye. It is constantly being produced behind the coloured bit of the eye, the iris. It then moves to the front of the iris and drains away just at the junction of the iris and the front of your eye. It is the balance of the fluid going in and going out that maintains the pressure. If it doesn't drain away quickly enough the pressure can build up, and if its too high that is indicative of glaucoma.
NON-CONTACT TONOMETER
The commonest way to measure the pressure is to use a non-contact tonometer. There are various different devices that do this. All of them, though, blow a wee puff of air onto your eye. It is actually measuring how long it takes to flatten a certain area of the eye, and then converts that into the pressure. When you get this done it does make you jump a bit. Don't worry about that, it is a perfectly natural reaction. Your brain doesn't know the difference between a potentially damaging foreign body or harmless puff of air going into the eye. So don't worry if you do jump, just try to keep your eye open before the air goes in.
Usually the optometrist will take three or four readings of the pressure to get an average value.
CONTACT TONOMETER
This requires the use of a local anaesthetic. The optometrist will put a drop in each eye. This might sting mometarily. They will also put an orange dye called fluorescein in your eye. Sometimes the anaethetic and dye are pre-mixed.
You might have to put your chin on a chin-rest or the optometrist might have a hand-held tonometer. They will then hold your eyelids open and then bring the tonometer forward to touch your eye. This is a small circular cone with a very bright blue light. It will only be held on your eye for a few seconds while the optom measures the pressure.
After the eydrops though you need to be careful not to rub your eyes while the anaesthetic is still working, as you could scratch your eye without realising it.
VISUAL FIELDS
This is the measure of how much you see round about you when looking straight ahead. It usually involves you looking at a central spot while some lights flash at the side. You may have to press a buzzer every time you see the light flash, or tell the optom how many spots of light you see. Most people over 60 have a screening visiual field test done.
A more in-depth test measures how bright a light needs to be for you to be able to see it. This test much more senstivie than whether you can see the light or not. The test can be quite arduous, especially if you are getting the in-depth test done. It takes four-six minutes each eye and so it can be hard to concentrate on the central spot all the ime.
PACHYMETRY
This measure how thick the cornea, the front surface of your eye, is. It is usually done at the same time as contact tonometry as the device has to touch your eye, so your eye needs to be anaethetised.
OPHTHALMOSCOPY
This happens at eevry sight test. The optom uses a special torch that focusses on different structures within the eye. They will come very close to you and the light will be very bright. It is with this that the optom will be able to check the nerve at the back of the eye, the place we look for glaucoma.
SLIT-LAMP BIOMICROSCOPY
If you are a bit older or the optom wants a better look you will have eye-drops instilled to make your pupils bigger. Once they have taken effect the optom will get you to put your chin on a rest and bring a small lens close to your eye. The light is very strong but it allows the optom to assess the optic disc in much better detail, and to assess the depth of the optic cup.
I know all this might sound a bit daunting but the tests are fine once you get started, and the optom will make them as easy for you as possible. It is so so important that you get regular checks.
I always start writing these blogs trying to simplify things and then seem to go on too much.
Next time I'll be brief.
Take care.
Best wishes,
Carla