Retinal ganglion cell topography and visual acuity of the sleepy lizard (Tiliqua rugosa)

The spatial distribution of retinal ganglion cells provides valuable insight into the importance species place on observing objects in specific regions of their visual field with higher spatial resolving power. We estimate the total number, distribution and peak density of ganglion cells in retinal wholemounts of the sleepy lizard, Tiliqua rugosa, a scincid lizard endemic to southern Australia. Ganglion cells were readily discernable from amacrine cells by their size and shape, prominent nuclei and the accumulation of Nissl-positive substances in their cytoplasm. A total of 1,654,200 (±59,400) presumed ganglion cells were estimated throughout the retina, distributed irregularly and forming a loose horizontal streak of high cell density peaking at 15,500 cells per mm(2). With a post nodal distance of 6.25 mm, we calculate an upper limit of visual acuity of 6.8 c/deg.