Br J Ophthalmol doi:10.1136/bjophthalmol-2013-304823
  • Laboratory science

The reliability of parafoveal cone density measurements

Open Access
  1. Joseph Carroll1,4,5,10
  1. 1Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
  2. 2Division of Biostatistics, Institute for Health and Society, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
  3. 3Program for Undergraduate Research, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
  4. 4Department of Biomedical Engineering, Marquette University, Milwaukee, Wisconsin, USA
  5. 5Departments of Cell Biology, Neurobiology & Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
  6. 6School of Optometry, University of California Berkeley, Berkeley, California, USA
  7. 7Institute of Optics, University of Rochester, Rochester, New York, USA
  8. 8Department of Ophthalmology, University of California San Francisco, San Francisco, California, USA
  9. 9Casey Eye Institute, Oregon Health & Sciences University, Portland, Oregon, USA
  10. 10Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
  1. Correspondence to Dr Joseph Carroll, Medical College of Wisconsin, The Eye Institute, 925 N. 87th Street, Milwaukee, WI 53226, USA; jcarroll{at}
  • Received 23 December 2013
  • Revised 17 March 2014
  • Accepted 29 April 2014
  • Published Online First 22 May 2014


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.

This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 3.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:

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