Visual field organization and retinal resolution in the beluga whale Delphinapterus leucas (Pallas).

Abstract

The distribution and size of ganglion cells in the retina of three retinal wholemounts of beluga whales ( Delphinapterus leucas )w ere investigated. Cell sizes were from 12 to 48 # mw ith monomodal size distribution. Ganglion cells concentrated at two spots of high density in the nasal and temporal quadrants, 50 to 60% from the optic disk. Both areas appeared as vertically elongated spots. The mean peak cell density over all wholemounts in the temporal and nasal areas was 400 and 300 cells/mm 2 , respectively. With ap osterior nodal distance of 12 m, these cell density corresponded to 17.4 cells/ deg 2 and 12.7 cells/deg 2 ,w hich provided an underwater retinal resolution of 14.4& (2.2 cycle/deg) and 16.9& (1.8 cycle/deg) in the temporal and nasal highdensity areas, respectively, and aerial resolution of 19.2& (1.6 cycle/deg) and 22.5& (1.3 cycle/deg). These data suggest that the beluga whale has slightly poorer visual acuity than other marine odontocetes investigated so far.