The distribution and size of ganglion cells in the retina of two tucuxi were investigated. Retinal cell size varied from 10 to 50 μm with a polymodal size distribution; major groups were seen with sizes of 8-20, 21-35, and more than 35 μm. Ganglion cells concentrated at two spots of the highest density in the nasal and temporal quadrants, about 10 mm (60′) from the optic disk. The mean peak cell density in both spots was 188-198 cells/mm2. With a posterior nodal distance of 9.5-10 mm (underwater), the density at those two spots corresponded to 5.4-5.7 cells/deg2, which provides a retinal resolution of 25′-26′ (1.16-1.19 cycle/deg) in water and 33′-34′ (0.9 cycle/deg) in air.