“After 60 minutes of defocus, ChT [choroidal thickness] increased by +8 ± 5 µm ( P < 0.001) with spherical myopic defocus, but varied with simple myopic astigmatic defocus, depending on the axis of astigmatism ( P < 0.001), increasing by +5 ± 6 µm ( P = 0.037) with WTR and decreasing by −4 ± 5 µm ( P = 0.011) with ATR astigmatic defocus.”
Another study showing similar results: https://www.sciencedirect.com/science/article/abs/pii/S0002939420303561
For folks with minus correction astigmatism closer to 0 or 180 axis, this would mean you’d experience WTR defocus without astigmatism correction. And if you were over prescribed with astigmatism correction at some point (my understanding is, correct me if I’m wrong), you would have experienced ATR defocus that your eyes potentially may have adapted to.
The evidence doesn’t prove much about how astigmatism progresses, but it makes me optimistic that astigmatic blur can and does physiologically change the eye in some way. Especially since these studies were conducted over the short term and this is an understudied topic. I’d be interested to see what effects choroidal thinning may have on eye aberrations and astigmatism in particular. I can only imagine that anything impacting blood flow and nutrients to the eye will have cascading effects on eye health.
Another interesting study looking at effects of high axial myopia (defined as -8D or worse): nature. com /articles/eye2013223#:~:text=Histological%20changes%20in%20high%20axial%20myopia%3A%20sclera&text=It%20showed%20that%20the%20high,posterior%20pole%20of%20the%20eye.
(remove spaces, I can only post 2 links per post)
they observed “a profound thinning of the choroid decreasing from ∼250 to <10 μ m in extreme axial myopia, secondary macular defects in the Bruch’s membrane associated with a complete loss of retinal pigment epithelium and choriocapillaris, and retinal photoreceptors…”