I don't think there is any causality between astigmatism and high blood pressure. But I do know there are many damages that high blood pressure might bring to us, including damages to eyes. Blood vessels are brittle, especially the blood vessels in eyes. The blood vessels in eyes are small so that they are invisible normally. The high blood pressure gives a great pressure on blood vessels so that the vessels might be broken or fluid might leak from the blood vessels, resulted in bleeding in eyes and fluid accumulated under the retina. It can also damages the optic nerves, by blocking the blood flow to eyes. While astigmatism is a refractive error related to genes, it can't be the result of high blood pressure. As to astigmatism, it is caused by uneven curvature. The light forms multiple focuses, resulted in blurry vision.