Corneal power (refraction) with and without corneal astigmatism, or is SE fixed?

Let’s say, corneal power is 43x45 D. Resulting refraction is Sph -3 Cyl -2.

So, if corneal astigmatism would go away, will cornea be:
a) SE - 44 D, refraction Sph -4
b) as past weakest meridian - 43 D, refraction Sph -3
c) as past strongest meridian - 45 D, refraction Sph -5

@Varakari, maybe you know?

Hey, necropost I know, but I’ve been rather busy… :sweat_smile:

Now, I really don’t know for sure, but if we assume that the cornea is pulled into shape by tension from its sides, and we’d be forming elliptical shapes of unchanging material properties into something more spherical again, it should be closer to the SE, as the cornea probably wouldn’t flatten or steepen overall.

So probably, the usual definition of SE as the true myopia value is a good one.

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Now I have opinion that a) or b), but rather not c).

I still believe the more power rectus muscles have, the more flat cornea (thus lower SE) is, because sometimes cornea compensates for difference between axial length and there is should be a reasonable mechanism for this.

I would vote for (natural) flatter corneas as they seem to be less prone to astigmatism.

And a flatter cornea has another side effect: it lets you see further, as it acts as a weaker lens, thus projecting (with the eye lens) the image of whatever you’re looking at a bit further back (for the same lens shape).

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