title: Optics of cone photoreceptors in the chicken (Gallus gallus domesticus).
abstract: Vision is the primary sensory modality of birds, and its importance is evident in the sophistication of their visual systems. Coloured oil droplets in the cone photoreceptors represent an adaptation in the avian retina, acting as long-pass colour filters. However, we currently lack understanding of how the optical properties and morphology of component structures (e.g. oil droplet, mitochondrial ellipsoid and outer segment) of the cone photoreceptor influence the transmission of light into the outer segment and the ultimate effect they have on receptor sensitivity. In this study, we use data from microspectrophotometry, digital holographic microscopy and electron microscopy to inform electromagnetic models of avian cone photoreceptors to quantitatively investigate the integrated optical function of the cell. We find that pigmented oil droplets primarily function as spectral filters, not light collection devices, although the mitochondrial ellipsoid improves optical coupling between the inner segment and oil droplet. In contrast, unpigmented droplets found in violet-sensitive cones double sensitivity at its peak relative to other cone types. Oil droplets and ellipsoids both narrow the angular sensitivity of single cone photoreceptors, but not as strongly as those in human cones.
authors.affiliation: School of Biological Sciences, University of Bristol, Bristol Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK Bristol Centre for Functional Nanomaterials, Centre for Nanoscience and Quantum Information, University of Bristol, Tyndall Avenue, Bristol BS8 1FD, UK david.wilby@bristol.ac.uk.
authors.forename: David
authors.identifier: http://orcid.org/0000-0002-6553-8739
authors.initials: D
authors.lastname: Wilby
authors.affiliation: Department of Pathology and Immunology, Washington University School of Medicine, St Louis, MO, USA.
authors.forename: Matthew B
authors.identifier: http://orcid.org/0000-0001-9184-197X
authors.initials: MB
authors.lastname: Toomey
authors.affiliation: Vision Group, Department of Biology, Lund University, Sölvegatan 35, Lund, Sweden.
authors.forename: Peter
authors.identifier: http://orcid.org/0000-0001-9026-3274
authors.initials: P
authors.lastname: Olsson
authors.affiliation: Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA, USA.
authors.forename: Rikard
authors.initials: R
authors.lastname: Frederiksen
authors.affiliation: Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA, USA.
authors.forename: M Carter
authors.initials: MC
authors.lastname: Cornwall
authors.affiliation: H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK.
authors.forename: Ruth
authors.identifier: http://orcid.org/0000-0003-1206-5357
authors.initials: R
authors.lastname: Oulton
authors.affiliation: Vision Group, Department of Biology, Lund University, Sölvegatan 35, Lund, Sweden.
authors.forename: Almut
authors.identifier: http://orcid.org/0000-0003-3937-2808
authors.initials: A
authors.lastname: Kelber
authors.affiliation: Department of Pathology and Immunology, Washington University School of Medicine, St Louis, MO, USA.
authors.forename: Joseph C
authors.identifier: http://orcid.org/0000-0002-9323-7140
authors.initials: JC
authors.lastname: Corbo
authors.affiliation: School of Biological Sciences, University of Bristol, Bristol Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK Bristol Centre for Functional Nanomaterials, Centre for Nanoscience and Quantum Information, University of Bristol, Tyndall Avenue, Bristol BS8 1FD, UK.
authors.forename: Nicholas W
authors.identifier: http://orcid.org/0000-0002-4540-6683
authors.initials: NW
authors.lastname: Roberts
mesh_terms: D000818:Animals; D002645:Chickens; D003116:Color; D060733:Electromagnetic Radiation; D006801:Humans; D008027:Light; D008855:Microscopy, Electron, Scanning; D015591:Microspectrophotometry / Q000379:methods*; D008954:Models, Biological; D015233:Models, Statistical; D009821:Oils; D055095:Optics and Photonics; D012031:Refractometry; D012160:Retina / Q000502:physiology; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D014785:Vision, Ocular
chemical_list: D009821:Oils
keywords: FDTD; birds; colour vision; cone; optics; photoreceptors