Abnormalities in the visual system of Xenopus after larval optic nerve section.

One optic nerve was cut in a series of larval Xenopus laevis; in approximately half of these the corresponding eye was also rotated. The resultant primary visual projections were mapped in the adult. Although in most cases the projections were retinotopically normal, some of them were not. These abnormal projections were consistently associated with a very thin optic nerve which reached the tectum via the oculomotor route. Animals with rotated eyes which developed retinotopically organised primary projections had a normal intertectal ipsilateral projection from the rotated eye and a rotated projection from the normal eye, thus confirming earlier findings that a process of binocular interaction determines the formation of intertectal connections. In all frogs with retinotopically abnormal primary projections the intertectal connections from the normal eye were of the type found after enucleation and those from the abnormal side were fragmentary or absent. Since the development of abnormal retinotopic patterns preceded that of intertectal connections the mechanisms of binocular interaction must have broken down in the presence of the abnormal primary projections.