This book offers a new critical edition, translation and commentary of the second maqÄla - on optics and theory of vision - of the 8th century AH/AD 14th century KitÄb nÅ«r al-Ê-uyÅ«n wa-ǧÄmiÊ- al-funÅ«n . The KitÄb nÅ«r alÊ-uyÅ«n wa-ǧÄmiÊ- al-funÅ«n is a significant medieval Arabic treatise on ophthalmology. This book focuses on the second "chapter" or maqÄla , which deals with optics and theories of vision. Readers will gain a new understanding of the treatment of optics in a late-medieval Arabic medical work; in particular, the adoption of mathematics in the work makes this unique in the context of medieval Arabic ophthalmology. The critical edition is accompanied by an English translation, detailed commentary, and introduction to the work that situates the work in its historical and intellectual context and offers important insights on a newly edited and translated source. This book is of interest to students and scholars working on the history of Arabic science, particularly optics and medicine, as well as historians of science more generally, codicologists, palaeographers, and those working on Arabic literary history.