Quantitative analysis of the retinal ganglion cell layer in the ostrich, Struthio camelus

The total number, distribution and peak density of ganglion cells were evaluated in the Nissl-stained retina of the ostrich (Struthio camelus). The mean (n = 4) total number of retinal ganglion cells (RGC) was estimated at 2,274,128 (s.d. = 273, 152). The ostrich retina exhibited a prominent horizontal visual streak along which a central area located nasal to the pecten had a peak density of 9,500 cells/mm2. A high concentration of cells with a peak density of 2,646 cells/mm2 was also observed in the temporal retina, slightly dorsal to the visual streak. The results further showed that the ostrich eye has a 15-mm pupil entrance diameter, its mean axial length is 39.81 mm, the estimated retinal magnification factor is 0.4075 mm/deg and the maximum visual acuity along the well-defined visual streak was estimated to be 19.32 cycles/deg. The latter component of the retina might subserve vision along the horizon while the temporal region mediates binocular processing. The data also showed that the degree of retinal illumination in this bird could be comparable to that noted in some nocturnal species. The findings in this study suggest that the ostrich might not be restricted to diurnal activity.