title: Eccentricity dependent changes of density, spacing and packing arrangement of parafoveal cones.
abstract: OBJECTIVE
  To investigate the distribution of cone density and spacing as well as the preferred packing arrangement of the cone mosaic as a function of retinal eccentricity.
  
  
  METHODS
  An adaptive optics retinal camera (rtx1, www.imagine-eyes.com) was used to obtain images of the parafoveal cone mosaic in nineteen healthy volunteers. Cone density and spacing were estimated for each subject (both eyes) using a sampling window of 80 × 80 pixels, at 250-, 450-, 650- and 1100-μm eccentricities from the fovea along the nasal and temporal retina of both eyes. The inter-subject and intra-subject variation of cone density and spacing were calculated via Coefficient of Variation (CoV). Cone packing arrangement was assessed using Voronoi analysis; calculations were done over 1024 × 128 pixels image sections of the cone mosaic across the horizontal meridian from 200- to 1050-μm eccentricities.
  
  
  RESULTS
  The inter-subject variation of parafoveal cone density ranged between 10% and 15% (p < 0.001) and the intra-subject variation of cone density was lower than 8% in all subjects, except for two. The cone spacing values showed a moderate inter-subject (CoV<7%; p < 0.001) and a low intra-subject variation (CoV<4% in all subjects, except for two cases). In the parafoveal region, 40-50% of cones were hexagonally arranged; the percentage of non-hexagonal Voronoi tiles increased at greater eccentricities.
  
  
  CONCLUSIONS
  The use of multiple and complementary metric descriptors allows for a more detailed description of packing distribution and preferred arrangement of cone photoreceptors across the parafoveal retina.
authors.affiliation: Fondazione GB Bietti IRCCS, Rome, Italy. mlombardo@visioeng.it
authors.forename: Marco
authors.initials: M
authors.lastname: Lombardo
authors.forename: Sebastiano
authors.initials: S
authors.lastname: Serrao
authors.forename: Pietro
authors.initials: P
authors.lastname: Ducoli
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Lombardo
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D002452:Cell Count; D006801:Humans; D012160:Retina / Q000033:anatomy & histology*; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology*; D014794:Visual Fields / Q000502:physiology*