Throughout medieval Islamic society, a medical pluralism existed as a continuum running from the formal theories and practices of learned medicine to those of local custom and magic. In the pre-Islamic Near East, there were medical concerns and practitioners who tended the needs of the sick and injured. For several centuries prior to the rise of Islam, Alexandria, as well as Rome, Constantinople, Antioch, Edessa, and Amida, had flourished as centers of scientific and medical activity. In the tenth and early eleventh centuries, several Arabic medical encyclopedias were composed that proved to be particularly influential in the learned medical tradition. Ophthalmology was the subject of specialized treatises and a topic in which medieval Islamic writers displayed considerable originality. The Arabic literature on pharmacology quickly assumed a different form from that inherited from the Hellenistic world. In contrast to ophthalmology and pharmaceutics, the Islamic writings concerned with anatomy remain quite conservative, deviating little from their Hellenistic models.