Ophthalmology Hunayn ibn Ishaq enriched the field of ophthalmology. His developments in the study of the human eye can be traced through his innovative book, "Book of the Ten Treatises of the Eye". This textbook is the first known systematic treatment of this field and was most likely used in medical schools at the time. Throughout the book, Hunayn explains the eye and its anatomy in minute detail; its diseases, their symptoms, their treatments. Hunain repeatedly emphasized that he believed the crystalline lens to be in the center of the eye. Hunain may have been the originator of this idea. The idea of the central crystalline lens was widely believed from Hunain's period through the late 1500s. He discusses the nature of cysts and tumors, and the swelling they cause. He discusses how to treat various corneal ulcers through surgery, and the therapy involved in repairing cataracts. "Ten Treatises on Ophthalmology" demonstrates the skills Hunayn ibn Ishaq had not just as a translator and a physician, but also as a surgeon. As a physician Hunayn ibn Ishaq's reputation as a scholar and translator, and his close relationship with Caliph al-Mutawakkil, led the caliph to name Hunayn as his personal physician, ending the exclusive use of physicians from the Bukhtishu family. Despite their relationship, the caliph became distrustful; at the time, there were fears of death from poisoning, and physicians were well aware of its synthesis procedure. The caliph tested Hunayn's ethics as a physician by asking him to formulate a poison, to be used against a foe, in exchange for a large sum. Hunayn ibn Ishaq repeatedly rejected the Caliph's generous offers, saying he would need time to develop a poison. Disappointed, the caliph imprisoned his physician for a year. When asked why he would rather be killed than make the drug, Hunayn explained the physician's oath required him to help, and not harm, his patients. He completed many different medical works that pushed the idea of treating medicine with the practice and art of physic treatments. Some of his medical works were pulled from Greek sources such as, Fi Awja al-Ma'idah (On Stomach Ailments) and al-Masail fi’l-Tibb li’l-Muta’allimin (Questions on Medicine for Students) and having these sources to drawn on keeps the original text clear. As a translator With the construction of the House of Wisdom, the Abbasid Caliph al Ma'mun wanted to have a place to gather world