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Improved sampling and analysis of images in corneal confocal microscopy

Summary

Introduction: Corneal confocal microscopy (CCM) is a noninvasive clinical method to analyse and quantify corneal nerve fibres in vivo. Although the CCM technique is in constant progress, there are methodological limitations in terms of sampling of images and objectivity of the nerve quantification. The aim of this study was to present a randomized sampling method of the CCM images and to develop an adjusted area‐dependent image analysis. Furthermore, a manual nerve fibre analysis method was compared to a fully automated method.

Methods: 23 idiopathic small‐fibre neuropathy patients were investigated using CCM. Corneal nerve fibre length density (CNFL) and corneal nerve fibre branch density (CNBD) were determined in both a manual and automatic manner. Differences in CNFL and CNBD between (1) the randomized and the most common sampling method, (2) the adjusted and the unadjusted area and (3) the manual and automated quantification method were investigated.

Results: The CNFL values were significantly lower when using the randomized sampling method compared to the most common method (p = 0.01). There was not a statistical significant difference in the CNBD values between the randomized and the most common sampling method (p = 0.85). CNFL and CNBD values were increased when using the adjusted area compared to the standard area. Additionally, the study found a significant increase in the CNFL and CNBD values when using the manual method compared to the automatic method (p ≤ 0.001).

Conclusion: The study demonstrated a significant difference in the CNFL values between the randomized and common sampling method indicating the importance of clear guidelines for the image sampling. The increase in CNFL and CNBD values when using the adjusted cornea area is not surprising. The observed increases in both CNFL and CNBD values when using the manual method of nerve quantification compared to the automatic method are consistent with earlier findings. This study underlines the importance of improving the analysis of the CCM images in order to obtain more objective corneal nerve fibre measurements.

Lay description Introduction

Corneal confocal microscopy (CCM) is a nonharmful clinical method to analyse and determine the quality of corneal nerve fibres directly on the surface of the eye. Although the CCM technique is in constant progress, there are methodological limitations, such as choosing which images to analyse and how to perform objective nerve quantification. The aim of this study was to present a randomized sampling method of the CCM images and to develop an adjusted area‐dependent image analysis for nerve quantification. Furthermore, a manual nerve fibre analysis method was compared to a fully automated method.

Methods

23 patients diagnosed with a nerve fibre disease in the small nerve fibres were investigated using CCM. The length of the nerve fibres and the number of branches in the corneal nerves were determined in both a manual and automatic manner. Differences in nerve fibre length and number of branches between (1) the randomized and the most common sampling method, (2) the adjusted and the unadjusted area and (3) the manual and the automated analysis method were investigated.

Results

The nerve fibre lengths were shorter when using the randomized sampling method compared to the most common method. There was no difference in number of branches between the two sampling methods. Both nerve fibre length and number of branches were increased when using the adjusted area compared to the standard area. Additionally, the study found an increase in both parameters when using the manual method compared to the automatic method.

Conclusion

The study demonstrated a difference between the randomized and the most common sampling method when measuring nerve fibre length, indicating the importance of clear guidelines for the image sampling. The increase in nerve fibre length and number of branches when using the adjusted area is not surprising. The observed increases in both parameters when using the manual method of nerve analysis compared to the automatic method are consistent with earlier findings. This study underlines the importance of improving the CCM technique in order to obtain trustworthy corneal nerve fibre measurements.

Authors:   E.L. SCHALDEMOSE, F.I. FONTAIN, P. KARLSSON, J.R. NYENGAARD
Journal:   Journal of Microscopy
Year:   2017
Pages:   n/a
DOI:   10.1111/jmi.12581
Publication date:   26-May-2017
Facts, background information, dossiers
  • nerves
  • image analysis
  • fibre analyses
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