Author Topic: SRAX attribute for keratoconus diagnosis  (Read 16547 times)

Forrest

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Re: SRAX attribute for keratoconus diagnosis
« Reply #15 on: November 25, 2013, 05:01:46 pm »
thank you very much Michael.

Michael

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Re: SRAX attribute for keratoconus diagnosis
« Reply #16 on: November 28, 2013, 11:04:12 am »
Hi Everyone,

I am trying to use the following page as a reference to create the KISA attribute in Medmont Studio:
http://www.keratoconus.com/resources/Kisa$25+Index.pdf

I am having a little trouble working out exactly which values they are using for some of the formula  [(K) x (I-S) x (AST) x (SRAX) x 100]/300.
Can someone please correct me on these variables:
K - They define this as an expression of central corneal steepening.  I assume this is the steepest K value for the 3mm zone?
AST - ?

There appears to be certain conditions under which a variable is set to 1. Do you have a clear description of when that is?

Kind Regards
Senior Software Engineer
Medmont Pty. Ltd.

dmw69

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Re: SRAX attribute for keratoconus diagnosis
« Reply #17 on: November 28, 2013, 03:15:17 pm »
Hi Michael,

First I need to say that I'm not an authority on this and all I know is from what I've read and copied from other websites:

The “K value” which quantifies the central steepening of the cornea. Averaging dioptric powers of videokeratograph rings 2, 3 and 4 [not sure which topographer they are referring to here] provides a value for consideration; 47.20 D or greater is suggestive of KC.
For K, if <47.2 then use 1. If >47.2 then use K-47.2

AST value
refers to keratometric astigmatism (AST=ASTigmatism). AST of >1.5D is suggestive of k/conus.

Use absolute values.


Michael

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Re: SRAX attribute for keratoconus diagnosis
« Reply #19 on: December 06, 2013, 10:06:23 am »
Hi Everyone,

Forrest has had a chance to look at the results from the KISA attribute and the values seem to vary wildly. The result can be anywhere from 1 to 30000%. This doesn't seem logical for a percentage based index. Does anyone have some previous data where they have already calculated the SRAX and KISA indices that we can use to verify our results?

Kind Regards

 
Senior Software Engineer
Medmont Pty. Ltd.

dmw69

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Re: SRAX attribute for keratoconus diagnosis
« Reply #20 on: December 06, 2013, 11:29:51 am »
Michael I don't know the answer and once again I'm no expert but in the pdf you provided it says that keratoconics had a mean KISA of 10,382, albeit with an SD of 11,206. So I don't think it's a percentage meaning "out of 100", I think it's a percentage meaning they multiplied the raw figure by 100 to eliminate fractions/decimals? The article says 100% was just their cutoff between diagnosed early keratoconus vs normal or undiagnosed suspects. If the mean & SD from the article are 10K & 11K then a KISA of 30K from one of Forrest's "worst" patients is only 2 SD's from the mean.

Sorry I haven't had a chance to install and run the KISA attribute on my system yet.

dmw69

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Re: SRAX attribute for keratoconus diagnosis
« Reply #21 on: May 03, 2014, 04:03:39 pm »
So Michael I have finally had a chance to use the new SRAX attribute to try out the KISA formula. I tested it on some known keratoconus topos, some known normal topos, and one patient with very suspicious topos but not formally diagnosed with k/conus (yet!). Based on my very small survey, it seems to work well to split the normals below 100 and the k/conus's above 100.

The KISA results were (right eyes only):
normal eyes: -0.064, -3.33, 18.928, 1.4
known keratoconus eyes: 135, 585, 1708.8, 1557.68
suspicious but not yet formally diagnosed (same patient): RE 177, LE 49.

For the "K" value I just used the average of the flat & steep sim Ks. The instructions I had found earlier on the web said, "For K, if <47.2 then use 1. If >47.2 then use K-47.2"... but this doesn't make sense because for a mean K of (say) 47.1 the "K" value to plug in becomes 1, but for a mean K of (say) 47.3 the "K" value to plug in becomes 0.1. So instead I decided "If >47.2 then use K-47.2+1".

I'm not sure how my results above reconcile with the PDF you found saying that keratoconics had a mean KISA of 10,382... maybe I'm just lucky and my keratoconic patients are all mild. But the 1708 is a 33yr old with cones of 57.7D and sim Ks of 58.3/55.3.

I'm not sure why the formula says to x100 then divide by 300, instead of just saying to divide by 3.

So once again I'm not an expert on the KISA but to me it seems to work pretty well thanks to the SRAX attribute you created. It would be good if any other people reading this could try out the proposed KISA formula from this thread on their known keratoconics, known normals, and borderline patients, & provide feedback.
« Last Edit: May 03, 2014, 04:05:15 pm by dmw69 »

VisionIsTheKey

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Re: SRAX attribute for keratoconus diagnosis
« Reply #22 on: October 18, 2016, 06:59:52 am »
Gathered some info from keratoconusinserts.com and came up with the following:

The “K value” which quantifies the central steepening of the cornea. Averaging dioptric powers of videokeratograph rings 2, 3 and 4 [not sure which topographer they are referring to here] provides a value for consideration; 47.20 D or greater is suggestive of KC.
For K, if <47.2 then use 1. If >47.2 then use K-47.2