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Comparative Study
. 2018 Jul-Sep;11(3):182-191.
doi: 10.1016/j.optom.2017.06.001. Epub 2017 Aug 7.

Comparison of manual & automated analysis methods for corneal endothelial cell density measurements by specular microscopy

Jianyan Huang  1 , Jyotsna Maram  1 , Tudor C Tepelus  1 , Cristina Modak  2 , Ken Marion  2 , SriniVas R Sadda  1 , Vikas Chopra  1 , Olivia L Lee  3
Affiliations
Comparative Study

Comparison of manual & automated analysis methods for corneal endothelial cell density measurements by specular microscopy

Jianyan Huang et al. J Optom. 2018 Jul-Sep.

Abstract
in English, Spanish

Purpose: To determine the reliability of corneal endothelial cell density (ECD) obtained by automated specular microscopy versus that of validated manual methods and factors that predict such reliability.

Methods: Sharp central images from 94 control and 106 glaucomatous eyes were captured with Konan specular microscope NSP-9900. All images were analyzed by trained graders using Konan CellChek Software, employing the fully- and semi-automated methods as well as Center Method. Images with low cell count (input cells number <100) and/or guttata were compared with the Center and Flex-Center Methods. ECDs were compared and absolute error was used to assess variation. The effect on ECD of age, cell count, cell size, and cell size variation was evaluated.

Results: No significant difference was observed between the Center and Flex-Center Methods in corneas with guttata (p=0.48) or low ECD (p=0.11). No difference (p=0.32) was observed in ECD of normal controls <40 yrs old between the fully-automated method and manual Center Method. However, in older controls and glaucomatous eyes, ECD was overestimated by the fully-automated method (p=0.034) and semi-automated method (p=0.025) as compared to manual method.

Conclusion: Our findings show that automated analysis significantly overestimates ECD in the eyes with high polymegathism and/or large cell size, compared to the manual method. Therefore, we discourage reliance upon the fully-automated method alone to perform specular microscopy analysis, particularly if an accurate ECD value is imperative.

Objetivo: Determinar la fiabilidad de la densidad celular endotelial corneal (ECD) obtenida mediante microscopio especular automático frente a métodos manuales validados y factores predictivos de la fiabilidad.

Métodos: Se capturaron imágenes nítidas de 94 controles y 106 ojos glaucomatosos con un microscopio especular Konan NSP-9900. Todas las imágenes fueron analizadas por examinadores expertos mediante el software Konan CellChek, utilizando los métodos automatizado total, semiautomático y de centrado. Se compararon las imágenes con bajo recuento celular (número de células <100) y/o córnea guttata con el método de centrado y centrado flexible. Se compararon las ECD, utilizándose el error absoluto para valorar la variación. Se evaluó el efecto de la ECD sobre la edad, el recuento celular, el tamaño celular y la variación del tamaño celular.

Resultados: No se observó diferencia significativa entre los métodos de centrado y centrado flexible en las córneas con guttata (p = 0,48) o baja ECD (p = 0,11). No se observó diferencia (p = 0,32) en cuanto a ECD en los controles normales < 40 años entre el método totalmente automatizado y el método de centrado manual. Sin embargo, en los controles mayores y en los ojos glaucomatosos, la ECD fue sobreestimada por el método totalmente automatizado (p = 0,034) y el método semiautomático (p = 0,025), en comparación al método manual.

Conclusión: Nuestros hallazgos muestran que los análisis automatizados sobreestiman considerablemente la ECD en los ojos con alto polimegatismo y/o gran tamaño celular, en comparación al método manual. Por tanto, no recomendamos confiar en el método totalmente automatizado por sí solo para realizar estudios mediante microscopio especular, particularmente en casos en que la precisión del valor de ECD sea imperativo.

Keywords: Automated method; Center Method; Corneal endothelial cell density; Densidad celular endotelial corneal; Flex-Center Method; Microscopio especular; Método automatizado; Método de centrado; Método de centrado flexible; Specular microscopy.

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Figures

Figure 1
Figure 1
Mean endothelial cell density (ECD) by manual, semi-automated (semi) and fully-automated (auto) methods in control and glaucomatous eyes.
Figure 2
Figure 2
Mean endothelial cell density (ECD) by manual, semi-automated (semi) and fully-automated (auto) methods in control’ eyes stratified by age.
Figure 3
Figure 3
(A) Representative sample cornea with larger cell size and low cell size variation (CV < 32), before (ungraded) and after fully-automated, semi-automated or manual grading. Endothelial cell density (ECD) error between manual methods is 1.4%. Compared to mean manual ECD, error with automated methods is reduced from 231% with the fully-automated method to 4.4% with the semi-automated method by the grader's manual correction of cell size (from “S”, as the default cell size with the fully-automated method, to “XL” selected in semi-automated method). (B) Representative sample cornea with polymegathism (CV ≥ 32) before (ungraded) and after automated or manual grading. Note how, with polymegathism, no single cell size option from the automated method accurately approximates the manual endothelial cell density (ECD) value [error ranging from 16.2% (M) to 43.7% (S) to 43.5% (L)]. + This is NOT the manufacturer's recommended practice for the given cornea.
Figure 4
Figure 4
Representative sample cornea with severe guttata (guttae covering >40% of the viewable field) resulting in a drastically low number of gradable cells (INP < 100) graded by different manual methods.
Figure 5
Figure 5
The Bland–Altman plots illustrate the level of agreement between the analysis methods for the evaluation of ECD in control eyes. The solid line represents the mean difference, and the dashed lines show the 95% limits of agreement.
Figure 6
Figure 6
The Bland–Altman plots illustrate the level of agreement between the analysis methods for the evaluation of ECD in glaucomatous eyes. The solid line represents the mean difference, and the dashed lines show the 95% limits of agreement.
Figure 7
Figure 7
The Bland–Altman plots illustrate the level of agreement between the analysis methods for the evaluation of ECD in corneas with guttata or low INP. The solid line represents the mean difference, and the dashed lines show the 95% limits of agreement.
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