So SPH reduction happens when pseudomyopia is relieved and active focus stimulates axial change. But how about the mechanism of action for CYL reduction?
(For simplicity’s sake, please assume regular corneal astigmatism, i.e., that the astigmatism is not due to an irregularity of the lens or eyeball, that the corneal axis and meridian are perpendicular to each other, and that the refraction varies smoothly between said axis and meridian.)
We know that simplistically speaking, when we reduce CYL (& correspondingly create the “spherical equivalent”), the received image, when inspected circularly, gradually cycles between undercorrection and overcorrection.
And the cornea is then supposed to reshape (by itself, with the assistance of the extraocular muscles, or however), thereby reducing the astigmatism.
But what exactly stimulates this to happen? Is the brain’s detection of the symmetry of the undercorrection vs. overcorrection (for astig reduction) analogous to active focus (for myopia reduction)?
With SPH reduction, blur adaptation (==> lack of active focus) is a real possibility that can hinder progress. Whereas for CYL reduction, is the corresponding adaptation to the over- and under-correction not an issue due to their cycling between each other (circularly across the visual field)?
Another question I’ve been wondering is, how does the reduction rate of astigmatism broadly compare with that of myopia?
I’ve tried to be clear and simple, but I do apologise if this posting is hard to parse.
Any insight or reference would be much appreciated!