Historical descriptions of nystagmus and abnormal involuntary eye movements in various ancient cultures

Original texts and expert translations from various ancient cultures covering a time span from the 2(nd) millennium BC to the ninth century AD were searched for historical observations of involuntary eye movements. Abnormal, spontaneous eye movements are an easily recognisable neuro-ophthalmological symptom that can be both congenital and acquired. Ocular oscillations termed 'hippos' by Hippocrates (460-370BC) and Galenos (129-216AD) are synonymous with nystagmus, a term first introduced in the eighteenth century. The original description of hippos suggests an innate onset, which retrospectively can be related to either congenital (infantile) nystagmus or continuous involuntary eye movements of the blind. Other descriptions of abnormal involuntary eye movements with different beating directions, possibly associated with vertigo, seizures or ear symptoms and their impact on patients' quality of life (e.g. oscillopsia, blurred vision) are preserved in many fragmentary ancient documents including papyrus scrolls and stone tablets from Egypt, Mesopotamia, India, China, Greece, Rome and the Middle East. Although the sparse original descriptions of the direction and type of eye movements may inspire daring medical interpretations, caution is required when attempting to assign them to distinct nystagmus forms according to our current clinical classification of ocular motor disorders.