Given his poor eyesight it is even more remarkable that he took up astronomy, but it has to be said that his eyesight continued to improve during the thirty years following the smallpox.
Given kanyang mahinang paningin na ito ay mas kapuna-puna na siya kinuha up astronomy, ngunit ito ay dapat sinabi na ang kanyang paningin habang patuloy na mapabuti ang mga sumusunod na tatlumpung taon na ang bulutong.