He wrote the landmark textbook on ophthalmology in medieval Islam, Notebook of the Oculists, for which he was known in medieval Europe as Jesu Occulist, with "Jesu" being a Latin translation of "Isa", the Arabic name for Jesus.
Ibn 'Isa is considered one of the most famous physicians of the tenth century. His famous Notebook of the Oculists combined information obtained from both Greco-Roman and Arab sources. The book encompassed information on treatment and classification of over one hundred different eye diseases. In the book, eye diseases were sorted by their anatomical location. The Notebook of the Oculists was widely used by European physicians for hundreds of years. Ibn Isa’s book was one of the first, along with Hunayn ibn Ishaq’s Ten Treatises on the Eye, to illustrate anatomy of the eye. Specifically, Ibn Isa illustrated the optic chiasm and brain. Ibn Isa was the first to describe and suggest treatment for an array of diseases. For example, he was the first to discover the symptoms of Vogt-Koyanagi-Harada syndrome (VKH) - ocular inflammation associated with a distinct whitening of the hair, eyebrows, and eyelashes. Ibn Isa was also the first to classify epiphora as being a result of overzealous cautery of pterygium. In addition to this pioneering description, Ibn Isa also suggested treatments for epiphora based on the stage of the disease – namely treatment in the early stages with astringent materials, for example ammonia salt, burned copper, or lid past and a hook dissection with a feathered quill for chronic stages of epiphora. Ibn Isa is also thought to be the first to describe temporal arteritis, although Sir Jonathan Hutchinson (1828–1913) is erroneously credited with this.
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