Figure 8: Schematic describing the representation of the visual field in the SC in different rodent models.

Capitals and lower case letters illustrate zones of the visual field and corresponding retinocollicular projections, which are relative to right and left retina, respectively. The subscript ‘i’ indicates the furthest point of the visual field represented through the nasal border of the ipsilateral-projecting VTC of the retina. In wild-type animals, the zone of binocularity seen by the temporal retina is uniquely represented in the anterior SC so that ipsilateral projections result in an opposing polarity of topographic map (nasal–temporal retina projecting to anterior–posterior SC) relative to contralateral projections (temporal–nasal retina projecting anterior–posterior SC). In animals that undergo eye enucleation at birth, the ipsilateral fibers project continuously in the SC from across the retina with two polarities: an appropriate retinotopic map for normal ipsilateral projections in the anterior SC (nasal–temporal retina projecting anterior–posterior SC) and some aberrant projections in posterior SC by nasal retinal axons. In our genetic lesion mutants (α-Del), contralateral projections form a generally appropriate topographic map, although less refined. In addition, they are unable to innervate the entire SC, leaving an anterior and posterior zone empty. Instead, RGC axons from the ipsilateral eye are occupying some of this empty space and form TZs in anterior and posterior SC, mapping according to contralateral retinotopic polarity. As a result, opposite temporal extremities of the visual fields (‘seen’ by the nasal poles of each retina) map adjacently in the posterior SC.