“A statistically significant correlation was found between the axis of compound myopic astigmatism and the long axis of myopic retinal degeneration (r=0.89, p<0.001) and with the deep axis of disc crescents (r=0.80, p <0.001). Astigmatism is likely to have an aetiopathogenic association with myopic fundal changes.”
Likely, corneal astigmatism from high myopia is not from cornea itself, but either due to weakness of third nerve rectus muscles pair (superior, inferior) or biochemical changes inside sclera/eye.
Funny that with overall vision worsening occurred 3 months ago, right eye SPH stayed the same, but CYL increased also with left SPH. I hypothesize that horizontal right eye muscles are in strain so they can’t easily relax, that’s why sphere stays the same, as only vertical muscles lose the tension when oblique muscles get tight even more. That somehow reminds me scoliotic spine, when the main curve reached excess, the secondary curve usually develops. Then, both curves getting worse, if loaded with symmetric load. Pretty similar to the work of muscles then.
Let’s think about lens-induced astigmatism.
A contact lens correction Sph -8 is given. No matter what sphere/distance add/subtract, lens-induced astigmatism case doesn’t match for this.
-8 cyl -1.75. Left eye has overcorrected Cyl up to 0.75 D, while Sph is undercorrected by 0.25-0.75 D. Right eye has overcorrected Sph by 0.25 D, undercorrected Cyl up to 1 D. Then, I use close-up or less-distance-than-should-be vision. Then, left eye gets myopic defocus (MD) on horizontal meridian (HM), if right eye gets MD on VM and no defocus on HM. If right tries to emmetropize VM, left VM gets HD and HM gets clear or even also HD. So yes, left eye could worsen this way.