Make sure your glasses and windscreen are very clean and free of stripes from wiping them. It'll not help with the astigmatism, but at least the glasses and the windscreen aren't making it worse.

Another thing to try is the various kinds of night glasses, My mom swears by those. As a last resort you can try untinted polarized sunglasses. While those do make your view less bright they also make it lower contrast which might help.