Prescription questions

If you got a prescription and the sphere was much too high. So they
wrote a new prescription with half of the sphere. Would that affect
the strength or position of the astigmatism part of the prescription
as well?

Also, If you put a minus .50 test diopter lens up in front of your
plus lens, is it just reducing your sphere by .50, or is it also
changing the strength or position of the astigmatism part of the
prescription as well?

(E-Mail Removed) wrote:
> If you got a prescription and the sphere was much too high. So they
> wrote a new prescription with half of the sphere. Would that affect
> the strength or position of the astigmatism part of the prescription
> as well?

I find it wise to keep the same spherical equivalent (basically a
means of comparing the spherical and astigmatic components)
the same if drastically altering either the spherical or cylinder of
the spectacle rx. But it's not as important with mild changes or
having a low astigmatic correction.

>
> Also, If you put a minus .50 test diopter lens up in front of your
> plus lens, is it just reducing your sphere by .50, or is it also
> changing the strength or position of the astigmatism part of the
> prescription as well?

Just reducing the sph by .50 only.

frank