title: The reliability of parafoveal cone density measurements.
abstract: BACKGROUND
  Adaptive optics scanning light ophthalmoscopy (AOSLO) enables direct visualisation of the cone mosaic, with metrics such as cone density and cell spacing used to assess the integrity or health of the mosaic. Here we examined the interobserver and inter-instrument reliability of cone density measurements.
  
  
  METHODS
  For the interobserver reliability study, 30 subjects with no vision-limiting pathology were imaged. Three image sequences were acquired at a single parafoveal location and aligned to ensure that the three images were from the same retinal location. Ten observers used a semiautomated algorithm to identify the cones in each image, and this was repeated three times for each image. To assess inter-instrument reliability, 20 subjects were imaged at eight parafoveal locations on one AOSLO, followed by the same set of locations on the second AOSLO. A single observer manually aligned the pairs of images and used the semiautomated algorithm to identify the cones in each image.
  
  
  RESULTS
  Based on a factorial study design model and a variance components model, the interobserver study's largest contribution to variability was the subject (95.72%) while the observer's contribution was only 1.03%. For the inter-instrument study, an average cone density intraclass correlation coefficient (ICC) of between 0.931 and 0.975 was calculated.
  
  
  CONCLUSIONS
  With the AOSLOs used here, reliable cone density measurements can be obtained between observers and between instruments. Additional work is needed to determine how these results vary with differences in image quality.
authors.affiliation: Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
authors.forename: Benjamin S
authors.initials: BS
authors.lastname: Liu
authors.affiliation: Division of Biostatistics, Institute for Health and Society, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
authors.forename: Sergey
authors.initials: S
authors.lastname: Tarima
authors.affiliation: Division of Biostatistics, Institute for Health and Society, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
authors.forename: Alexis
authors.initials: A
authors.lastname: Visotcky
authors.affiliation: Program for Undergraduate Research, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
authors.forename: Alex
authors.initials: A
authors.lastname: Pechauer
authors.affiliation: Department of Biomedical Engineering, Marquette University, Milwaukee, Wisconsin, USA.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Cooper
authors.affiliation: Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
authors.forename: Leah
authors.initials: L
authors.lastname: Landsem
authors.affiliation: Departments of Cell Biology, Neurobiology & Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Wilk
authors.affiliation: Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
authors.forename: Pooja
authors.initials: P
authors.lastname: Godara
authors.affiliation: School of Optometry, University of California Berkeley, Berkeley, California, USA.
authors.forename: Vikram
authors.initials: V
authors.lastname: Makhijani
authors.affiliation: Institute of Optics, University of Rochester, Rochester, New York, USA.
authors.forename: Yusufu N
authors.initials: YN
authors.lastname: Sulai
authors.affiliation: Department of Ophthalmology, University of California San Francisco, San Francisco, California, USA.
authors.forename: Najia
authors.initials: N
authors.lastname: Syed
authors.affiliation: Department of Ophthalmology, University of California San Francisco, San Francisco, California, USA.
authors.forename: Galen
authors.initials: G
authors.lastname: Yasumura
authors.affiliation: Casey Eye Institute, Oregon Health & Sciences University, Portland, Oregon, USA.
authors.forename: Anupam K
authors.initials: AK
authors.lastname: Garg
authors.affiliation: Casey Eye Institute, Oregon Health & Sciences University, Portland, Oregon, USA.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Pennesi
authors.affiliation: School of Optometry, University of California Berkeley, Berkeley, California, USA.
authors.forename: Brandon J
authors.initials: BJ
authors.lastname: Lujan
authors.affiliation: Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA Department of Biomedical Engineering, Marquette University, Milwaukee, Wisconsin, USA Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Dubra
authors.affiliation: Department of Ophthalmology, University of California San Francisco, San Francisco, California, USA.
authors.forename: Jacque L
authors.initials: JL
authors.lastname: Duncan
authors.affiliation: Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA Department of Biomedical Engineering, Marquette University, Milwaukee, Wisconsin, USA Departments of Cell Biology, Neurobiology & Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin, USA Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
authors.forename: Joseph
authors.identifier: http://orcid.org/0000-0002-8640-1029
authors.initials: J
authors.lastname: Carroll
mesh_terms: D000328:Adult; D002452:Cell Count; D005260:Female; D005584:Fovea Centralis / Q000166:cytology*; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D019721:Ophthalmoscopes / Q000592:standards*; D009887:Ophthalmoscopy / Q000379:methods*; D010363:Pattern Recognition, Automated / Q000379:methods; D015203:Reproducibility of Results; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology*; D012164:Retinal Diseases / Q000175:diagnosis; D055815:Young Adult
keywords: Anatomy; Imaging; Retina