How to measure positive astigmatism?


The tool we have to measure astigmatism (print and build) seems to be oriented for negative astigmatism as it says to push imagem back until we see blur.

How to measure for hipermetropia cases?

If the astigmatism is + but your overall correction in -
then the astigmatism correction is still probably a minus, just less minus than the rest.

So if you had -4.00 sph diopters, and +1.00 cyl diopters at 90 degree axis,
then that is like saying “along 90 degree axis, have 1 less diopter of strength”
which is like saying “along 180 degree axis, have 1 more diopter of strength”.
But, if you change from + cyl to - cyl, it is not only the axis that changes,
but the overall sph correction as well.
This is because you are using a lower baseline sph correction with one part a bit stronger,
instead of a higher baseline correction with one part a bit weaker.

Here is an online tool that will make the conversion for you. :slight_smile:

If, on the other hand, you had -2 sph, and +3 cyl, then your astigmatism would actually be plus.
But I don’t know if that is a realistic example.

Another website this is worth looking at is this one, which explains how to make the change without an online calculator:

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My daughter (7 years old) has +0.75 SPH and at least +2.00 CYL (measured in the ophthalmologist), but when I try to measure with the she actually says that she sees better when puting very close!

As all measures are hypermetropic I’m confused… as I would expect for the far away the better…

Is the use of the word degree intentional here?