J.L. Prévost, Eye Deviation, and Early Steps in Space Lateralization: "Looking At or Away"

Conjugate deviation of the eyes toward side of lesion was recognized over a century ago as a manifestation accompanying hemiplegia, usually of apoplectic origin. While working on the services of Alfred Vulpian and Jean-Martin Charcot, Jean-Louis Prévost sparked international interest in the neurologic sign later named after him. His 1868 thesis represents the first systematic case series of patients with this ocular sign, observed in conjunction with head rotation toward the nonparalyzed side, which he called conjugate deviation (CD) of the eyes. Within a decade, it was uniformly reported in both French and English medical literature. Ipsilesional deviation was the rule for cortical or subcortical paralytic lesions. Contralesional deviation, more rarely seen, signaled lesions of lower brain regions, particularly pontine, or indicated irritative, excitatory effects (as in Jacksonian epilepsy). The sign was recognized to be a valuable diagnostic aid in unilateral cerebral lesions. Centralized control of CD by specific cerebral sites, such as frontal, or occipital, or oculomotor centers, was explored, along with the complex relationship with hemineglect, which interestingly was reported only several decades later. The discovery of intricate oculomotor interconnections and self-space relationships, which play an essential role in CD, owes much to Prévost and his followers.