Hi , Has anybody had a problem actually seeing the red square in middle of chequer board ? I kept staring at it and it disappeared started going darker first. The nurse that took test seemed concerned Is this normal ?
Hi,
that happened to me too.I think might be a bit of an optical illusion created by the moving / flickering checks (I think)
try not to read too much into nurses responses. when i had visual evoked potentials done i also had legs and feet done too. when the nurse came to put the sensor / stimulator thing on my foot, she initially couldnt get my foot to respond at all. i got a bit worried because she seemed to be looking quite concerned about it… then she worked out that the part of the foot / nerve she was looking for was just hiding behind a bit of muscle… and the test went fine from there. I think what I perceived as her being ‘concerned’ was actually her just concentrating on doing the test. It is tempting to try and ‘read minds’ of nurses, especially when you are really wanting answers about what is going on. but try not to read too much into nurses responses, unless they tell you outright that something is unusual or that they are concerned…
I am not sure but I think the red square is just your eye getting used to the differing light situation and shouldn’t be there. See http://www.mult-sclerosis.org/VisuallyEvokedResponse.html as the other anon says I wouldn’t worry about it and ask Neuro when you see him/her.
G
Hi Nlambe
You probably got a nurse who knows how to administer the VEP Test, but does not know the underlying science.
The big thing about the VEP is that you do not have to do anything - the electrodes pick up your responses to the changing pattern of squares (chequerboard).
You were told to look at/concentrate on.or some similar words that meant stare at the red square.
Human optics are very complicated, but what is really wanted is that your eyes stay looking in the same direction.
If you do, then some of the visual processes will change the actual colour that you see, starting with the brightness of that red square. Think Optical Illusions here.
This does not really affect the test, which is really concerned with finding out if a change of stimulus (chequerboard) produces a change of signal strength across the electrodes.
So, is there a change, how fast does it happen, how big is it - these are all questions that can be answered as long as you are looking roughly at the centre of the pattern.
The changing perception of the red square was enough for you to mention it - and the nurse did not know why.
If it was an old system with a CRT Monitor (i.e. not a flat screen) then there could be a few more things that could happen that the nurse would not be aware of as well.
But, overall, do not worry about it.
Geoff
Hi Nlambe
You probably got a nurse who knows how to administer the VEP Test, but does not know the underlying science.
The big thing about the VEP is that you do not have to do anything - the electrodes pick up your responses to the changing pattern of squares (chequerboard).
You were told to look at/concentrate on.or some similar words that meant stare at the red square.
Human optics are very complicated, but what is really wanted is that your eyes stay looking in the same direction.
If you do, then some of the visual processes will change the actual colour that you see, starting with the brightness of that red square. Think Optical Illusions here.
This does not really affect the test, which is really concerned with finding out if a change of stimulus (chequerboard) produces a change of signal strength across the electrodes.
So, is there a change, how fast does it happen, how big is it - these are all questions that can be answered as long as you are looking roughly at the centre of the pattern.
The changing perception of the red square was enough for you to mention it - and the nurse did not know why.
If it was an old system with a CRT Monitor (i.e. not a flat screen) then there could be a few more things that could happen that the nurse would not be aware of as well.
But, overall, do not worry about it.
Geoff