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.