title: In vivo measurements of cone photoreceptor spacing in myopic eyes from images obtained by an adaptive optics fundus camera.
abstract: OBJECTIVE
  To determine the cone spacing in normal and myopic eyes from the images obtained by an adaptive optics (AO) fundus camera.
  
  
  METHODS
  Nineteen eyes of 19 healthy volunteers with a mean +/- SD spherical equivalent refractive error of -3.7 +/- 3.3 diopters (D) (range, -0.3 to -11.1 D) and a mean axial length of 25.4 +/- 1.61 mm (range, 23.4-28.0 mm) were investigated in a prospective cross-sectional study. An AO fundus camera equipped with a liquid crystal phase modulator was used to obtain the images of the photoreceptor mosaic. The spacing between the cones was calculated manually at a retinal locus 2 degrees temporal from the center of the fovea. The magnification of the image was calculated by the axial length measured with an IOL Master.
  
  
  RESULTS
  The axial length was correlated with the refractive error (Pearson, r = -0.869; P < 0.001). The average cone spacing in the moderate- to high-myopia group (-6.5 +/- 2.3 D, n = 9) was 4.71 +/- 0.44 microm, which was significantly greater (P = 0.002) than the 3.90 +/- 0.47 microm in the normal and low-myopia groups (-1.1 +/- 0.9 D, n = 10). The cone spacing was significantly correlated with the axial length (r = 0.77, P < 0.001).
  
  
  CONCLUSIONS
  The AO fundus camera is capable of acquiring images of the photoreceptors in normal and myopic eyes. The greater spacing between cones in the myopia group is consistent with histological findings. These results suggest that retinal expansion should be considered in addition to Knapp's law when aniseikonia is evaluated in axial myopia.
authors.affiliation: Department of Applied Visual Science, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Kitaguchi
authors.forename: Kenichiro
authors.initials: K
authors.lastname: Bessho
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: Naoki
authors.initials: N
authors.lastname: Nakazawa
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Mihashi
authors.forename: Takashi
authors.initials: T
authors.lastname: Fujikado
mesh_terms: D000328:Adult; D001837:Body Weights and Measures; D002452:Cell Count; D003430:Cross-Sectional Studies; D003941:Diagnostic Techniques, Ophthalmological; D006801:Humans; D008875:Middle Aged; D009216:Myopia / Q000150:complications*; D010781:Photography / Q000379:methods*; D011446:Prospective Studies; D017949:Retinal Cone Photoreceptor Cells / Q000473:pathology*