IMHO, given the head is upside down, the ciliary muscle of the eye is having more difficulties for to freely adjust the crystalline lens due the blood pressure

IMHO, given the head is upside down, the ciliary muscle of the eye is having more difficulties for to freely adjust the crystalline lens due the blood pressure increment. So I think the effect described in the article sounds more like a lack of strength, or a strength adapted to lower pressure conditions, while adjusting the lenses. has this been checked?