Application of the After-Image Test in the Investigation of Squint

The visual act in strabismus has been for a long time a controversial subject for partisans of the so-called empirical and nativistic doctrines, the former headed by Helmholtz, the latter by E. Hering. Helmholtz regarded the vision in strabismus to be a strong argument in favor of attributing the sensory correspondence of the two eyes to training and learning, referring to the fact that not only have patients with squint no diplopia but sometimes they even display rudiments of binocular cooperation. On the other hand, the nativistic theory, starting out from indisputable anatomic facts, such as the semidecussation of the optic nerves and the hemianoptic scotomas resulting from a lesion on one side of the calcarine cortex, claims that there is an innate basis for the sensorial relationship between the two retinas. Indeed, the old theory of retinal identity taught by Johannes Müller has been given up. E. Hering showed