Optimal image sample size for corneal nerve morphometry

Dimitrios Vagenas, Nicola Pritchard, Katie Edwards, Ayda M. Shahidi, Geoff P. Sampson, Anthony W. Russell, Rayaz Malik, Nathan Efron

Research output: Contribution to journalArticle

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PURPOSE.: Arbitrary numbers of corneal confocal microscopy images have been used for analysis of corneal subbasal nerve parameters under the implicit assumption that these are a representative sample of the central corneal nerve plexus. The purpose of this study is to present a technique for quantifying the number of random central corneal images required to achieve an acceptable level of accuracy in the measurement of corneal nerve fiber length and branch density. METHODS.: Every possible combination of 2 to 16 images (where 16 was deemed the true mean) of the central corneal subbasal nerve plexus, not overlapping by more than 20%, were assessed for nerve fiber length and branch density in 20 subjects with type 2 diabetes and varying degrees of functional nerve deficit. Mean ratios were calculated to allow comparisons between and within subjects. RESULTS.: In assessing nerve branch density, eight randomly chosen images not overlapping by more than 20% produced an average that was within 30% of the true mean 95% of the time. A similar sampling strategy of five images was 13% within the true mean 80% of the time for corneal nerve fiber length. CONCLUSIONS.: The "sample combination analysis" presented here can be used to determine the sample size required for a desired level of accuracy of quantification of corneal subbasal nerve parameters. This technique may have applications in other biological sampling studies.

Original languageEnglish
Pages (from-to)812-817
Number of pages6
JournalOptometry and Vision Science
Issue number5
Publication statusPublished - May 2012
Externally publishedYes



  • corneal confocal microscopy
  • corneal nerves
  • diabetes
  • sampling methodology

ASJC Scopus subject areas

  • Ophthalmology
  • Optometry
  • Medicine(all)

Cite this

Vagenas, D., Pritchard, N., Edwards, K., Shahidi, A. M., Sampson, G. P., Russell, A. W., Malik, R., & Efron, N. (2012). Optimal image sample size for corneal nerve morphometry. Optometry and Vision Science, 89(5), 812-817. https://doi.org/10.1097/OPX.0b013e31824ee8c9