It is a matter of common experience that if one looks at a brightly illuminated surface like the sky, small dancing spots can be seen. These usually appear as bright circles against a somewhat darker background ; occasionally, the shape is more oval, and one side is brighter than the other. In every case, these spots are highly motile and pursue more or less definite paths, which are usually short and somewhat curved.
This phenomenon was first described by Boissier de Sauvages1 in 1763, and was thought by him to have some connection with the circulation of blood in the retina. In 1813, Steinbuch2 likewise gave a good description of the movements which he noticed when he looked at an illuminated blank wall and pressed gently on the eye. Purkinje,3 in 1819, pointed out that any circulatory disturbance caused by bodily movements or fever made the spots