I have a basic understanding of myopic spherical and cylinder
correction.  I am curious as to the algorithm used by the optometrist or
 opthalmologist ( which is better, "1" or "2") for converging on the
proper prescription.  Is the best spherical only correction determined
first?  And then how would a test for cylinder be done?  Is it added or
subratcted from the spherical? And initially at what axis?  And if the
axis is 90 degrees out, how is the need for a cylinder correction
ascertained?  And then how does the examiner converge on the magnitude
and axis of the cylinder?

I don't know if this is a naive question, but in summary.... is there a
simple "algorithm" to follow in a simple refraction to converge on the
proper sphere and cylinder/axis?  Or a web site link describing such an
algorithm?

Thanks for any responses; I have always wondered about this.

Bob