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K. M. Bumsted O'Brien, A. Querubin, J. M. Provis; Morphological Analysis of the Adult and Developing Pigeon (Columba livia) Fovea. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2139.
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In some species, the best visual acuity is achieved by the fovea centralis, a small pit where the inner retinal neurons have been pushed aside, rods are missing and cones are packed at their highest density. This study aims to characterise the morphological development of the pigeon fovea and to map the photoreceptor and ganglion cell topography in the adult retina.
A series of eyes from developing pigeons at embryonic day (E) 8, 10, 12, 14 and 1 week post-hatch and 10 adult pigeons (Columba livia) were fixed in 4% paraformaldehyde. Flatmounted eyes were used for photoreceptor density counts and rod opsin immunocytochemistry. Frozen sections were labelled with rod opsin and stained with Propidium Iodide to determine photoreceptor and ganglion cell densities, or were stained with Cresyl violet for morphological analysis.
By E10 and at all older ages, the pigeon fovea was detected 1.5mm nasal to the optic disc. The early fovea was characterized by cones forming a single layer of cuboidal cells and doming of the ganglion cells at the fovea. As development proceeded, cone density increased in the fovea and the ganglion cells began to move laterally forming a pit, although the adult fovea was never completely excavated. In the adult pigeon retina, cone photoreceptor and ganglion cell densities peaked at 326,000 and 110,000 cells/mm2 , respectively, in the rod-free fovea. Outside the fovea, in the yellow field, rod density remained constant, while cone and ganglion cell densities decreased toward the periphery.
These data demonstrate that pigeon foveal development follows a morphological progression similar to primate foveal formation. In the adult pigeon, regional variations in cell density focussed on the fovea, correlate well with regions of high acuity. Therefore, the pigeon fovea is a good model for primate foveal development in that it shares a number of important morphological and functional characteristics.
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