Authors: Mindaugas Mitkus Sandra Chaib Olle Lind Almut Kelber
Publish Date: 2014/03/28
Volume: 200, Issue: 5, Pages: 371-384
Abstract
Retinal ganglion cell RGC isodensity maps indicate important regions in an animal’s visual field These maps can also be combined with measures of focal length to estimate the theoretical visual acuity Here we present the RGC isodensity maps and anatomical spatial resolving power in three budgerigars Melopsittacus undulatus and two Bourke’s parrots Neopsephotus bourkii Because RGCs were stacked in several layers we modified the Nissl staining procedure to assess the cell number in the wholemounted and crosssectioned tissue of the same retinal specimen The retinal topography showed surprising variation however both parrot species had an area centralis without discernable fovea Budgerigars also had a putative area nasalis never reported in birds before The peak RGC density was 22300–34200 cells/mm2 in budgerigars and 18100–38000 cells/mm2 in Bourke’s parrots The maximum visual acuity based on RGCs and focal length was 69 cyc/deg in budgerigars and 92 cyc/deg in Bourke’s parrots These results are lower than earlier behavioural estimates Our findings illustrate that retinal topography is not a very fixed trait and that theoretical visual acuity estimations based on RGC density can be lower than the behavioural performance of the birdWe would like to thank members of Lund Vision Group for practical support and ongoing discussions We thank Carina Rasmussen and Eva Landgren for sharing their knowledge and technical guidance in histology Financial support from the Royal Physiographic Society in Lund and the Swedish Research Council Stockholm Grant 62120095683 is gratefully appreciated
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