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. 2017 Aug 17;12(8):e0183040.
doi: 10.1371/journal.pone.0183040. eCollection 2017.

Corneal confocal microscopy is a rapid reproducible ophthalmic technique for quantifying corneal nerve abnormalities

Alise Kalteniece  1 , Maryam Ferdousi  1 , Safwaan Adam  1 , Jonathan Schofield  1 , Shazli Azmi  1 , Ioannis Petropoulos  2 , Handrean Soran  1 , Rayaz A Malik  1   2
Affiliations

Corneal confocal microscopy is a rapid reproducible ophthalmic technique for quantifying corneal nerve abnormalities

Alise Kalteniece et al. PLoS One. .

Abstract

Purpose: To assess the effect of applying a protocol for image selection and the number of images required for adequate quantification of corneal nerve pathology using in vivo corneal confocal microscopy (IVCCM).

Methods: IVCCM was performed in 35 participants by a single examiner. For each participant, 4 observers used a standardized protocol to select 6 central corneal nerve images to assess the inter-observer variability. Furthermore, images were selected by a single observer on two occasions to assess intra-observer variability and the effect of sample size was assessed by comparing 6 with 12 images. Corneal nerve fiber density (CNFD), branch density (CNBD) and length (CNFL) were quantified using fully automated software. The data were compared using the intra class correlation coefficient (ICC) and Bland-Altman agreement plots for all experiments.

Results: The ICC values for CNFD, CNBD and CNFL were 0.93 (P<0.0001), 0.96 (P<0.0001) and 0.95 (P<0.0001) for inter-observer variability and 0.95 (P<0.0001), 0.97 (P<0.001) and 0.97 (P<0.0001) for intra-observer variability. For sample size variability, ICC values were 0.94 (P<0.0001), 0.95 (P<0.0001), and 0.96 (P<0.0001) for CNFD, CNBD and CNFL. Bland-Altman plots showed excellent agreement for all parameters.

Conclusions: This study shows that implementing a standardized protocol to select IVCCM images results in high intra and inter-observer reproducibility for all corneal nerve parameters and 6 images are adequate for analysis. IVCCM could therefore be deployed in large multicenter clinical trials with confidence.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Examples of CCM images.
A) a high quality CCM image of sub basal nerves from the central cornea (nerves are vertical); B) A CCM image with a pressure line (indicated with an arrow); C) A CCM image of sub basal nerves from the peripheral cornea (oblique nerves); D) a CCM image with overlapping corneal layers (stroma and sub-basal nerve plexus) as can be seen with the keratocytes in the inferior and peripheral zone; E) a low contrast CCM image; F) inferior whorl of the cornea.
Fig 2
Fig 2. Summary plot of ICC values for all experiments in relation to reliability of assessment of CCM parameters.
Fig 3
Fig 3
Bland-Altman agreement plots; first row, inter-observer reliability (OB1a and OB2a) for CNFD (A), CNBD (B) and CNFL (C); second row, Intra-observer repeatability (OB2a vs OB2b) for CNFD (D), CNBD (E), CNFL (F) and sample size validity (OB1a and OB1b) for CNFD (G), CNBD (H) and CNFL (I).
See this image and copyright information in PMC

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