In this paper, “anisopia” is understood to be unequal vision in the two eyes producing unequal imagery; anisopia can be either inherently existing or artificially introduced. The term imagery is defined to encompass the complexity of physical, chemical, neuro-biochemical, and physio-psychological processes within the eye, the visual pathway, and the visual center in the cortical zone. A great variety of physical, physiological, and psychological factors are capable of producing anisopia which manifests itself as a characteristic distortion of space because of angular disparity of apparent contours. This anisopic stereo-effect can best be observed by the use of two individual square targets lying in a fronto-parallel plane; the effect consists of an apparent rotation of the individual targets about individual vertical axes. The anisopic stereo-effect is related to changes in the perceptual image size which is altered as a result of anisopia. An analysis of anisopia and its significance in vision is attempted, and experiments dealing with anisopia produced by monocular application of neutral density filters, spherical and cylindrical lenses, pupillary diaphragms, and bleaching of the retina are described.