Ocular Anatomy, Ganglion Cell Distribution and Retinal Resolution of a Killer Whale <b><i>(Orcinus orca)</i></b>

Abstract

Retinal topography, cell density and sizes of ganglion cells in the killer whale (Orcinus orca) were analyzed in retinal whole mounts stained with cresyl violet. A distinctive feature of the killer whale’s retina is the large size of ganglion cells and low cell density compared to terrestrial mammals. The ganglion cell diameter ranged from 8 to 100 µm, with the majority of cells within a range of 20–40 µm. The topographic distribution of ganglion cells displayed two spots of high cell density located in the temporal and nasal quadrants, 20 mm from the optic disk. The high-density areas were connected by a horizontal belt-like area passing below the optic disk of the retina. Peak cell densities in these areas were evaluated. Mean peak cell densities were 334 and 288 cells/mm² in the temporal and nasal high-density areas, respectively. With a posterior nodal distance of 19.5 mm, these high-density data predict a retinal resolution of 9.6′ (3.1 cycles/deg.) and 12.6′ (2.4 cycles/deg.) in the temporal and nasal areas, respectively, in water.

Características Morfológicas de la Retina del Calderón Común (Globicephala melas; Traill, 1809) y su Relación con el Hábitat

“…Dichas células han sido descritas en todos los mamíferos marinos estudiados a excepción del delfín de río Platanista gangética, cuyas células miden alrededor de 20 micras: Balaenoptera physalus (Pillery & Wandeler, 1964), Tursiops truncatus Mass & Supin, 1995), Delphinus delphis (Dral, 1983), Phocoena phocoena (Mass et al, 1986), Balaenoptera acutorostrata (Murayama et al, 1992), Eschrichtius gibosus (Mass & Supin, 1997). El tamaño de estas células contrasta con el de los mamíferos terrestres, de aproximadamente 25 µm en algunos casos (Hughes, 1975(Hughes, , 1981.…”

Retinal Topography in Two Species of Baleen Whale (Cetacea: Mysticeti)

“…After dissecting away excess extraocular tissue, the axial diameter of each eye (measured from the external surface of the cornea to the external surface of the thickened sclera [Mass and Supin, 1997;Buono et al, 2012]), and the naso-temporal and dorso-ventral diameters of both the eye and the cornea were measured to the nearest Mass and Supin [2002]. This species has two specialised areas of high cell density, one in the nasal part of the retina, and one in the temporal part of the retina.…”

“…Having said this, our knowledge of the visual capabilities of cetaceans comes primarily from studies of small odontocetes, such as the porpoises and dolphins (Table 1) [e.g., Spong and White, 1971;White et al, 1971;Herman, 1990Herman, , 2010Mobley and Helweg, 1990;Tomonaga et al, 2014], which, being much smaller than mysticetes, can thus be more readily kept in captivity and used in psychophysical experiments. It is also possible to more readily collect well-preserved tissue from odontocetes that die in captivity, or from animals that become stranded [Murayama and Somiya, 1998;Mass and Supin, 1995;Mass et al, 2013]. In contrast, collecting eyes that are preserved well enough for histological analysis from larger species is far more problematic.…”

“…1; Table 1). In contrast to the odontocetes, retinal topography has been described in just two species of mysticete, the grey whale, Eschrichtius robustus, and the minke whale, Balaenoptera acutorostrata [Mass and Supin, 1997;Murayama et al, 1992] (Table 1). However, both species have a very similar retinal topography to that described for odontocetes, despite the significant differences in, for example, body size and shape, feeding strategy and behavioural ecology between the two clades.…”

Retinal Ganglion Cell Topography and Retinal Resolution in the Baikal Seal <b><i>(Pusa sibirica)</i></b>

“…This similarity to terrestrial carnivores is characteristic of pinnipeds but not of other aquatic mammals. Cetaceans (both odontocetes and mysticetes) have two high-resolution retinal areas, one in the nasal and the other in the temporal quadrant of the retina [Dral, 1977[Dral, , 1983Gao and Zhou, 1987;Mass and Supin, 1995, 2002Murayama et al, 1995;Murayama and Somiya, 1998;Supin et al, 2001;Mass et al, 2013]. Another aquatic mammal, the manatee ( Trichechus manatus , Sirenia), has neither a definite area centralis nor a visual streak [Mass et al, 2012].…”