past pointing and nystagmus

[Ramoray]

i have a question that i cannot figure out or find anywhere. In brs neuro page 207 it talks about caloric stimulation and past pointing. The previous section talks about postrotational testing. Spinning a person to the right causes slow eye movements to left ( VOR) and past pointing and falling to the right, which makes sense as i tried spinning around to the right and yes you do point to right and fall that way. however i dont understand the cold water caloric stimulation results- since cold water in the left ear for example simulate the same movments in that ear as happens in spinning to the right, therefore you have slow movements to the left with fast nystagmus to the right. which makes sense but then it says that upon caloric stimulation of the left ear you have past pointing to the same side(left) which makes no sense because if it is supposedly making the same changes as happense in spinning to the right why wouldnt you also past point to the right just like you do when you really do spin to the right? sorry not a great explanation but maybe some neuro guru out there can help me! id much appreciate it! thanks!

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[smgilles]

i have a question that i cannot figure out or find anywhere. In brs neuro page 207 it talks about caloric stimulation and past pointing. The previous section talks about postrotational testing. Spinning a person to the right causes slow eye movements to left ( VOR) and past pointing and falling to the right, which makes sense as i tried spinning around to the right and yes you do point to right and fall that way. however i dont understand the cold water caloric stimulation results- since cold water in the left ear for example simulate the same movments in that ear as happens in spinning to the right, therefore you have slow movements to the left with fast nystagmus to the right. which makes sense but then it says that upon caloric stimulation of the left ear you have past pointing to the same side(left) which makes no sense because if it is supposedly making the same changes as happense in spinning to the right why wouldnt you also past point to the right just like you do when you really do spin to the right? sorry not a great explanation but maybe some neuro guru out there can help me! id much appreciate it! thanks!

If I am reading your questions correctly, which I am not sure that I am. It is because Cold water in the caloric test will cause (fast phase) nystagmus in the opposite side. So if you put cold water in the LEFT ear it will cause fast phase nystagmus to the RIGHT and slow phase to the left. If you were to use warm water then the fast phase would be to the same ear you induced the warm water.

If you have a comatosed patient and use the caloric test and the slow phase is intact but there is no fast phase, then you know the brainstem is intact since the vestibular system controls the slow phase.

If you have a comatosed patient and use the caloric test and the fast phase is intact but there is no slow phase then you know the cortex is intact since you use the frontal eyefields for the fast phase.

Hope this helps and I hope I answered your question.

 

[Ramoray]

If I am reading your questions correctly, which I am not sure that I am. It is because Cold water in the caloric test will cause (fast phase) nystagmus in the opposite side. So if you put cold water in the LEFT ear it will cause fast phase nystagmus to the RIGHT and slow phase to the left. If you were to use warm water then the fast phase would be to the same ear you induced the warm water.

If you have a comatosed patient and use the caloric test and the slow phase is intact but there is no fast phase, then you know the brainstem is intact since the vestibular system controls the slow phase.

If you have a comatosed patient and use the caloric test and the fast phase is intact but there is no slow phase then you know the cortex is intact since you use the frontal eyefields for the fast phase.

Hope this helps and I hope I answered your question.

I actually was just asking about the past pointing with caloric testing but thanks .And actually it is impossible to have a fast phase in tact with no slow phase because with no brainstem it doesnt matter if the cortex is in tact because although the cortex iniates the fast signal it still needs the brainstem to carry out the command(needs the pprf and mlf) so that waasnt tru but if you have any insight on pastpointing directiosn with caloric stim. that would be great! thanks!

 

[NR117]

Ramoray, I know this still doesn't answer your question in the original post but just for clarification of caloric testing in coma:

With a comatose patient, you NEVER have fast phases. Those fast phases are refixation eye movements, they are initiated by the slow phases; and the patient has to be trying to fixate on an object to have them. In other words you don't see the nystagmus when the patient is comatose. What you DO see with an intact brainstem is a tonic deviation which is a slow phase. If there is no deviation then you know the brainstem reflexes are gone.