RESUMO
This article addresses the practical aspect of medieval Arabic medicine by examining ophthalmological fragments of the Cairo Genizah, written between the tenth and thirteenth centuries. This article deals with two issues: (1) the logic behind the actual preparation of compound medicines and (2) the logic behind the entire treatment process. The first issue is examined by investigating recipes of eye medicines for leucoma (bayad) recorded in genizah notebooks. By examining the four primary qualities of each ingredient, I clarify how the actual prescription of compound medicines has been grounded in the four-quality theory. The second issue is examined from a reading of two genizah letters. These letters suggest that diagnostic theory actually provided the framework for the analysis of the symptoms. The diagnoses determined medieval ophthalmologists' selection of eye medicines and their method of application.