Contrary to popular belief, chinchillas do not have a pure rod retina

Purpose: To establish whether there is cone contribution to retinal function and structure in chinchillas (Chinchilla lanigera), in view of the prevailing notion that this species possesses a pure rod retina. Methods: Photopic electroretinography (ERG) responses to high-intensity flashes (10 and 25 cd*s/m²) were recorded unilaterally in six pigmented chinchillas following 10 minutes of light adaptation (30 cd/m²). Retinas of two animals were studied histologically, and immunohistochemistry (IHC) was conducted to detect the presence of short and medium/long wavelength cone photoreceptors. Results: ERG recordings revealed photopic responses, albeit of low amplitudes. Histopathology demonstrated presumptive cone inner segments in the photoreceptor layer. Presence of cone photoreceptors was confirmed by IHC. Cone density was higher in the central retina, and red/green cones outnumbered blue cones. Conclusions: Our results provide convincing evidence for the presence of functioning cone photoreceptors in the chinchilla retina, disproving the established belief that the species has a pure rod retina.