Pope John XXI was an ophthalmologist before becoming Pope. He was born in Lisbon and trained at University of Paris and was part of the early medical school faculty in Siena. He became physician for Pope Gregory X and shifted to church duties. He rose quickly in the ranks of the Catholic church and was elected Pope in 1276 AD. His term was short. He died when construction in the Papal Palace at Viterbo, collapsed on him. His text book is in two parts with introductions to the eye followed by descriptions of diseases with their mostly medical treatments. He concludes with a section about his own wonderful waters. The work survived and a copy was even found amongst Michelangelo's papers. Unfortunately the book turns out to be a plagiarism of two earlier text books. His most notable achievement supposedly was discovering that glaucoma was a disease with a hard eye. It turns out that this section is referring only to a suppurative external disease with indurated lids called sclerophthalmia.