Possible Sampling Error in Corneal Specular Microscopy: Can Central Endothelial Data Generated by Specular Microscope Represent the Real Clinical Condition of the Whole Cornea?

Abstract

Purpose: To estimate the minimum number of cells required to obtain reliable data in a specular microscope, which could possibly represent the real clinical condition of the corneal endothelium. Methods: A cross-sectional study of 122 eyes of 61 individuals submitted to noncontact specular microscope was conducted. Data generated by the manufacturer's software were uploaded to specific statistical software for sampling relative error calculation. When relative error was above 5%, new images were acquired and more cells counted until the desired relative error was reached. Data analyzed in this study for the desired relative error were number of cells marked by the examiner for each eye (marked cells), number of cells used for data analysis (analyzed cells), endothelial area used for analysis, sampling error, and absolute number of images used for each eye. Results: The average number of marked cells required to obtain a relative sampling error of less than 5% was 425.2 ± 102.2 cells. The average number of analyzed cells used by the specular microscope to generate the data was 247.4 ± 51.6 cells. The average endothelial area of the analyzed cells was 0.43 ± 0.08 mm2. The mean sampling error was 3.7% ± 0.6%, and an average of 2.95 ± 0.74 images was needed to obtain a relative sampling error of less than 5%. Conclusions: We conclude that, theoretically, a minimum of 425.2 cells from 2.95 images must be marked to obtain reliable results, which could possibly represent the real endothelial clinical condition of the whole cornea.

Assessment and Correlation of Corneal Endothelial Cell Changes in Different Stages of Keratoconus in Non–contact Lens Wearers

“…None of the previous studies have mentioned about the number of cells analyzed and the cell area required to obtain representative sample of corneal endothelial cells. Few other studies have speculated that a minimum selection of more than 100 cells with equal or very similar numbers for each eye is required to obtain reliable results 26,27 . Otherwise, the data might be inaccurate, as it is not truly representative of the endothelial mosaic because very little area and few cells are used to represent the corneal endothelial profile.…”

Correlation between ocular biometric parameters and corneal endothelium in a sample of young Egyptian adults

“…Nevertheless, it is recommended that the same device is used when examining changes in the same eye at different time points [ 21 ]. Recently, it has been shown that single central endothelial measurements may constitute a sampling error and may not provide a comprehensive overview of the corneal condition, and that an average of at least 2.9 images is needed to obtain reliable results [ 22 ].…”

Corneal Endothelium Viability Assay Using Trypan Blue Dye After Preloaded DMEK Graft Preparation

“…7 In addition, recent research suggests that significant changes in cell density are not observed immediately after DMEK preparation and that specular samples commonly analyzed by eye banks may not be representative of global ECD. 8…”

“…7 In addition, recent research suggests that significant changes in cell density are not observed immediately after DMEK preparation and that specular samples commonly analyzed by eye banks may not be representative of global ECD. 8 At Eversight, compliance with medical standards was achieved by performing specular microscopy immediately after DMEK graft preparation but before injector loading. This step-wise approach required the prepared tissue to be returned to a corneal viewing chamber for specular image capture and then removed for loading into the injector, which was inefficient and time consuming.…”