A curiously interesting episode that deserves a place in the history of Papal Physicians occurred during Alderotti’s life. One of the Popes elected to fill the Papal chair had been earlier in life a physician. This was the famous Peter of Spain, though he was really a Portuguese, who, under the name of John XXI., occupied the Papal throne during the years 1276-1277. Peter of Spain had been one of the most distinguished natural scientists of this interesting century. Dr. J. B. Petella, in an article published in Janus about ten years ago, entitled A Critical and Historical Study of the Knowledge of Ophthalmology of a Philosopher Physician who became Pope, gives an excellent account of the life of Pope John XXI.
Petella does not hesitate to say of him that he was “one of the most renowned personages of Europe during the thirteenth century, from the point of view of the triple evolution of his extraordinary mind, which caused him to make his mark in the physical sciences, in the metaphysical sciences, and in the religious world. In him there was an incarnation of the savant of the time, and he must be considered the most perfect encyclopedist of the Middle Ages in their first renascence.”
Anyone who reads Dr. Petella’s account of this book by Pope John XXI. will be surprised at how much was known about diseases of the eye at the middle of the thirteenth century. For instance, hardening of the eye is spoken of as a very serious affection, so that there seems to be no doubt that the condition now known as glaucoma was recognized and its bad prognosis appreciated. His account of the external anatomy of the eye, eight coats of which he describes, beginning with the conjunctiva and ending with the retina, is quite complete. The eye is said to have eight muscles, the levator of the upper eyelid and the sphincter muscle of the eye being counted among them. The other muscles are picturesquely described as reins, that is, guiding ribbons for the eye. Cataract is described as water descending into the eye, and two forms of it are distinguished–one traumatic, due to external causes, and the other due to internal causes. Lachrimal fistula is described and its causes discussed. Various forms of blepharitis are touched upon. Many suggestions are made for the treatment of trichiasis. That a man who was as distinguished in medicine as Peter of Spain should have been elected Pope, is the best possible proof that there was no opposition between science and religion during the thirteenth century.
James J. Walsh, The Popes and Science (1908)