Strabismus was a known eye misalignment since the Hippocratic era (ca 5th century BC). Hippocrates and his followers were the first to introduce the hypothesis of a hereditary condition. Many ancient Greek physicians like Galen (ca 2nd AD) provided several definitions, while Paul of Aegina (625-690 AD) was the scholar who introduced a method to treat it. Paul used a full face mask and an oil lamb to guide the eyeballs toward the desired direction. It seems that this approach endured for centuries to come. During 11th century AD in Constantinople, the Byzantine scholar and politician Michael Constantine Psellus (ca 1020-1105 AD) composed a series of philosophical, religious, political and scientific treatises. Among his work stands a medical iambic didactic poem of 1732 lines, in which he had mentioned strabismus. Although he was not an oculist, he had managed to define strabismus. His definition was noted as such, "Strabismus is caused by a spasm of the bodies which move (the eye balls) and the oblique tendency of the muscles". Psellus was aware of the knowledge of the past and recorded what was still valid at that era, presenting a memorable definition. As his reference was completely neglected from the medical bibliography, our study aims to add him in the scientific chain of those who understood this disorder. This study aims to compose Psellus biography, present ancient Greek and Byzantine ophthalmology's opinion concerning strabismus and note Psellus' definition. The TLG and MedLine/PubMed databases were searched and the terms "strabismus" and "Psellus" were used as key words.
Keywords: Byzantine medicine; Michael constantine psellus; ophthalmology; strabismus.