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Post Info TOPIC: Hysteresis-A new unit of measurment


Phase Two

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Date: Sat Oct 21 11:09 AM, 2006
Hysteresis-A new unit of measurment
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OK, what is a Hysteresis? and why has this measurment just been discovered and is needed?


No googling for the answer! (and its likely not to be there) as if you was paying attention you guys should know of the top of your heads! (OK very newbies may not know!)


 



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Executive

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Date: Sun Oct 22 12:34 AM, 2006
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Quintrix it concerns the ORA measurment. Take a look here

Ocular Response Analyzer presentation

Cornea is a visco-elastic system. It reacts in its own specific way on a mechaniical load/perturbation/ stress. Normal corneas are more rigid than ours. Thus their response time to a very fast mechanical act of pressure is faster: corneal surface gets the load in, takes time, comes back to the previous position. There is a difference between the time it comes in and the time it comes back. This may be called a hysteresis. In our corneas this time is bigger I think, because cornea is less rigid, more viscous. It is not very precise what I say but the general intuition is like that. So the number captures the difference between week conreas and normal ones. In fact it may be used before LASIK like surgeries to tell which people can do it which can not. In KC corneas it is about 8. In normal ones it is about 12. Cros-linking shifts us from 8 to 12.

-- Edited by Yarsky at 00:35, 2006-10-22

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yarsky


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Date: Sun Oct 22 2:47 AM, 2006
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Dear friends,


ORA is a very new machine which is spreeding through hospitals in the world. This a slight air pulse. The machine makes four measures of CH and give a mean of these four ones which permits to value the rigidity of the cornea, which was not possible before this invention.


In my case, before C3R, my right had a CH of 8,3, one week afterwards the operation, it was 8,9 and one month afterwards, it was 9,9. Doctors told me the mean value in the population was 11.


This machine seems very interesting to follow a C3R and perhaps, in the future, it will permit to know when it is required to make a new C3R before risking a regression.


Time will permit to learn how much reliable and precise is the machine. Perhaps, will it possible to make some relations between KC severity, evolution speed and ORA...


Best regards.



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Phase Two

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Date: Mon Oct 23 7:15 PM, 2006
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The invention of the ORA has given us a new measurement of the cornea called "Hysteresis"


Thanks Yarsky and Action for your thoughts on this, this machine has come at the right time, it all seems to be coming together. It's a great feeling to know people are "on the ball" and developing technology which makes a new measurment of something that could not be measured before, thats the hardness/softness of the cornea. Its one of those technologies that those serious with your treatment will have, as it will not make them more money having this machine but it will be usful for better diagnoses and monitoring of cases.


I only mentioned this machine to a professional at an eye center, the next time I was there they had it!!


I would like to see the results of testing what the Hysteresis is on Intacts, mini-ark, X linking (and the different ways that it is done). Also used in pre-lazer screening, as the weakness/strenghtness of the cornea certainly done matter in this case!


Action was you tested with the ORA? and was that done in France? I think you may very well get more strenghtening in the months to come. Good to hear from you.


Best



-- Edited by QuintriX at 19:19, 2006-10-23

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Date: Tue Oct 24 2:18 AM, 2006
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Dear Quintrix,


I did ORA before and after in C3R in France (this not available in Paris, so I went to Toulouse  (5outh of France) where study of 20 patients is led). A strengthening effect took place before C3R, my CH value was 8,3 and at my last control (one month after C3R) the value was 9,9. The machine can certainy do mistake but doctors told me they could not be such important. However, improvement on topography could not be seen.


Like you, I hope the strengthening effect will become more important, however this was not the point of view of the profesor who told me that cross-links creation in the cornea had taken place immediately during the time of the operation and, as a consequence, he coiuld not understand how C3R could have some effects several months after this operation. However, litterature reports some improvements some months later so C3R has certainly some effects after operation, it remains to understand why.


Best regards.


 


 



-- Edited by Action444 at 02:18, 2006-10-24

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Phase Two

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Date: Tue Oct 24 6:18 AM, 2006
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At the lecture I went to about X Linking, they explained that the links created are a bit like comparing it to braces you wear on your teeth, in your mouth to straighten teeth. It takes time for the teeth to "move" towards the right direction, it is not instant, but slow for tissue to be incouraged to take up its new location. There may well be only very slight improvments in vision after crosslinking, the main thing, as you know, is to stop KC, so the earlier its done the better.


Having said all that, at the lecture, they did say that even if there was hardly no change on topography, it was clear that contrast sensitivity improved quite a bit, here in London, months after patients did X Linking. So something was happening with-in the cornea. So was it due to fibers coming together due to the braces effect, or shrinking of the collegan fibers with in the cornea? Its probably both I think as B2 very much helps for both to happen.



-- Edited by QuintriX at 06:20, 2006-10-24

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