Quantitative and topographical study of retinal ganglion cells in the chameleon (Chameleo chameleon).

Chameleons display a number of well-described physiological peculiarities of their visual system, but there is no information on the topography of the retinal ganglion cell layer. In the present study, ganglion cell density of the chameleon retina was constructed from whole mounts of the retina stained with cresyl violet. For the identification of ganglion cells, these latter cells were labelled retrogradely with horseradish peroxidase applied to the optic nerve. Using this criterion, the proportion of ganglion cells was estimated to represent 80% of retinal cells, while glial cells and amacrine cells represented 14 and 6%, respectively, of the total cell population of the retina. As for the main features of the retinal map, first, ganglion cells were distributed inhomogeneously within the ganglion cell layer, and revealed the existence of a putative area centralis. Second, a horizontal visual streak, which showed two peak density areas, was identified. These features point out the degree of specialisation of the chameleon retina and the complexity of its visual system.