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Rania A. Masri, Paul R. Martin, Ulrike Grunert; Topography of cone bipolar cells in human retina. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2997. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
A map of the inner human retina is necessary to guide target areas for treatment in retinal diseases, and to better support current diagnostic tools. The aim of this study was to perform a quantitative analysis of bipolar cells involved with high acuity and colour vision (flat midget bipolar, FMB), and the diffuse bipolar cells involved motion detection (DB3a,b).
Post mortem human donor eyes (n=4, aged 40–60 years) were obtained from the Lions NSW Eye Bank at Sydney Eye Hospital with ethical approval. Retinas were fixed in 2% paraformaldehyde and pieces of defined eccentricity from temporal retina were embedded in Agarose and sectioned vertically along the horizontal meridian using a Vibratome. The sections were double or triple labeled using cell-type specific immunohistochemical markers; FMB cells were labeled using antibodies against recoverin, and DB3a and DB3b cells were labeled with antibodies against calbindin and CD15, respectively. Antibodies against cone arrestin (kindly provided by Peter McLeish) were used to label cone photoreceptors and antibodies against the RNA binding protein RBPMS were used to label ganglion cells. Sections were imaged using a confocal microscope and cell populations were counted across the length and depth of the section.
The density of FMB cells is roughly five times higher than the diffuse bipolar cells at all eccentricities. At 1 mm eccentricity, the average density of FMB cells is 30,500 (± 4600) cells/mm2 whereas the density of DB3a and DB3b cells is 6,500 (± 2300) and 5,500 (± 1900) cells/mm2 respectively. We also quantified the density of cone photoreceptors and ganglion cells relative to the bipolar cell interneurons in the same preparation. At 5 mm eccentricity, the density of FMB cells is 9,100 cells/mm2; cone photoreceptor density is 8,100 cells/mm2 and ganglion cell density is close to 1,800 cells/mm2. The ratio of FMB cells to cone photoreceptors is 1:1 up to at least 10 mm eccentricity.
Our results indicate a differential distribution of the bipolar cells involved in acuity (FMB) and motion (DB3a,b) detection pathways in the retina. The matched density of cone photoreceptors to midget bipolar cells implies one-to-one connectivity outside the fovea, meaning single-cone signals can reach the inner plexiform layer.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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