Comparison of the Center and Flex-Center Methods of Corneal Endothelial Cell Analysis in the Presence of Guttae

Comparison of automated corneal endothelial cell analysis in healthy and postoperative eyes with phakic intraocular lens: a cross-sectional study and literature review

PURPOSE

Measurement of corneal endothelial cells is critical for postoperative evaluation of phakic intraocular lens (pIOL) surgery. However, inter-instrument differences in corneal endothelial cell density (ECD) after pIOL implantation have not yet been reported. This study aimed to compare automated corneal endothelial cell analysis between CellChek-20 (Konan Medical, Hyogo, Japan) and EM-4000 (Tomey, Nagoya, Japan) in healthy and postoperative eyes with pIOL.

METHODS

We retrospectively analyzed 154 healthy and 236 postoperative eyes after pIOL surgery. Endothelial cell measurements were performed using CellChek-20 and EM-4000 with autofocusing and automated image analysis. ECD, percentage of hexagonal cells (HEX), coefficient of variation in cell size (CoV), and central corneal thickness (CCT) were compared between the two devices.

RESULTS

The ECDs of the two devices were highly correlated in both healthy (Spearman's correlation coefficient [r] = 0.805; p < 0.001) and postoperative (r = 0.901; p < 0.001) groups. ECD from CellChek-20 was higher than EM-4000 in both healthy (mean difference = 228.9 cells/mm2; p < 0.001) and postoperative (mean difference = 115.6 cells/mm2; p < 0.001) groups. The CCT values also showed a strong correlation in healthy eyes (r = 0.974; p < 0.001) and in postoperative eyes (r = 0.936; p < 0.001); however, significant inter-instrument differences were observed. HEX and CV showed significant differences and relatively weak correlations (r < 0.7) between the two devices in both healthy and postoperative groups.

CONCLUSION

The ECD values between the two instruments were correlated, but that of the CellChek-20 was significantly higher than that of the EM-4000 in both healthy and postoperative eyes after pIOL surgery. Most previous studies have also shown that the Konan software overestimated the ECD compared to other products in automatic measurement mode. The possibility of measurement bias should be considered when replacing equipment used for corneal endothelial cell measurements.

Corneal endothelial validation in the eye bank: differences in automated methods and repeatability

PURPOSE

To evaluate reproducibility of endothelial cell density (ECD) measurements using the Konan Cell Check D in donor corneas by two different ophthalmologists and to compare the two automated cell count methods (center and flex-center) available in the software of this specular microscope.

METHODS

ECD values were quantified in 54 donor corneas by two independent investigators using the Cell Check D (Konan Medical USA Inc) with both automated cell count methods. In the center method, at least 30 contiguous cells are marked. For the flex-center method, an area is delineated and only the cells within the designated area are counted.

RESULTS

The mean ECD was 2473.81±378.22 cells/mm2. Good ECD intergrader reproducibility for the center (ICC=0.821) and the flex-center method (ICC=0.784) were noted. Poor reliability was observed for coefficient of variation and hexagonality (ICC≤0.265). When both methods for ECD analysis were compared, a moderate correlation for the two independent graders using the two manual (center and flex-center) methods was detected (correlation coefficient of 0.678 and 0.745 for each of the investigators). Comparison between methods yielded significantly higher ECD with the flex-center method (P=0.013). When corneas were divided by ECD, those under 2200 cells/mm2 and those between 2200 and 2700 cells/mm2 also had significantly higher ECD with the flex-center method (P<0.022).

CONCLUSIONS

ECD values are reproducible with both methods, although the flex-center method ECDs tend to be higher, particularly in cases of low ECD. Eye banks and surgeons should exercise caution in making decisions based only on small differences in ECD.

Overestimation of corneal endothelial cell density by automated method in glaucomatous eyes with impaired corneal endothelial cells

PURPOSE

To determine between-method differences in corneal endothelial cell parameters using center and automated methods of non-contact specular microscopy (CellCheck software of Konan, Inc.) in glaucomatous eyes.

METHODS

We analyzed the central corneal endothelial cell density (ECD) of 245 glaucomatous eyes using center (ECD-Ce) and automated methods (ECD-Au). Based on the ECD-Ce, we allocated subjects to Groups 1 to 10 (at 250 cells/mm2 intervals) and evaluated the ECD, coefficient of variation in cell area (CV), and percentage of hexagonal cells (HEX).

RESULTS

There was a close correlation (r = 0.91) between the ECD values measured using both methods. However, ECD-Au were significantly higher than those measured by the center method when ECD-Ce was less than 2500 (in Groups 1 to 8; P < 0.001 to P = 0.006). The regression equation of (ECD-Au-ECD-Ce) = 1028-0.397*ECD-Ce shows greater deviation in eyes with lower ECD, and this difference became 0 when ECD -Ce was 2593 cells/mm2. None of the 44 subjects with an ECD-Ce of < 1000 cells/mm2 recorded an ECD-Au < 1000 cells/mm2. Compared with the center method, the automated method had higher and lower median CV and HEX values, respectively (P < 0.001). The between-method differences in both CV and HEX were negatively correlated with ECD-Ce (r = -0.49, P < 0.001 and r = -0.25, P < 0.001, respectively).

CONCLUSION

The automated method of the CellCheck software overestimates ECD in eyes with lower ECD values and may overlook risk of corneal decompensation.

Agreement of Corneal Endothelial Cell Analysis Between Konan-Noncon Robo SP-6000 and Tomey EM-3000 Specular Microscopes in Healthy Subjects

PURPOSE

To compare corneal endothelium parameters taken by two common noncontact specular microscopes in healthy subjects.

METHODS

Healthy participants visiting the outpatient eye clinic at the Rabin Medical Center, Petah Tikva, Israel, were recruited prospectively. All participants underwent three consecutive corneal endothelial cell photographs with both the Konan-Noncon Robo SP-6000 and the Tomey EM-3000 specular microscopes. Endothelial cell density (ECD) was evaluated using the manual center technique in both machines. Bland-Altman graphs were used to assess the agreement between the devices, and intraclass correlation coefficient (ICC) served to assess intraobserver variability for each device.

RESULTS

Recruited were 49 healthy subjects with a mean age of 48.9±15.6 years, 49 right eyes were included. The mean ECD was comparable between the Tomey EM-3000 and the Konan-Noncon Robo SP-6000 (2,713.2±242.4 vs. 2,700.8±300.5 cells/mm2, respectively, P=0.47) with a mean difference of 12.4 cells/mm2 (0.67%), a mean ECD absolute difference of 93.3 cells/mm2, and low 95% limits of agreement of -222.0 to +246.9 cells/mm2. A folded empirical distribution function curve showed that all differences fell within 525.4 cells/mm2, centered around a median of 13.3 cells/mm2. Intraclass correlation coefficient was high for both the Konan-Noncon Robo SP-6000 (0.93, 95% confidence interval [CI]: 0.89-0.95) and the Tomey EM-3000 (0.88, 95% CI: 0.82-0.93).

CONCLUSIONS

The difference in endothelial cell measurements between the Konan SP-6000 and the Tomey EM-3000 specular microscopes through the center and the L-count analyzing techniques, respectively, is clinically small and not statistically significant. Nevertheless, caution should be taken when used interchangeably because ECD difference between the two machines can be as high as 525.4 cells/mm2.

Discrepancies in Endothelial Cell Density Values of Human Donor Corneas Resulting From Comparison Between Specular Microscopes and Endothelial Analysis Methods

PURPOSE

The methods for specular microscopy evaluation across eye banks differ, which may result in variability in endothelial cell density (ECD) values that influence the surgeon's decision about donor tissue. A comparison of instruments and analysis methods is conducted in this study.

METHODS

Specular images were captured from 97 donor corneas using both HAI and Konan specular microscopes. A single best quality image of each cornea from each instrument was graded using the respective inherent software and analysis method (HAI: variable frame method; Konan: center method). All raw specular images were standardized for dimensions and regraded in the CellChek system in a blinded fashion. The grading variances and paired t test were performed between instruments in both inherent and standardized analyses. Correlation and Bland-Altman analyses between instruments were also performed.

RESULTS

Using the software inherent within HAI and Konan, the mean ECD readings for the 97 corneas were 2764 ± 583 and 2605 ± 517 cell/mm (P = 0.045), respectively, with a variance of 8.05% (range 0.26%-27.2%). HAI resulted in a higher ECD value in 79 corneas (81.4%). In CellChek software analysis, the mean ECD readings did not differ (2609 ± 514 and 2496 ± 507 cells/mm, respectively, P = 0.127), with a variance of 5.6% (range 0.24%-19.8%).

CONCLUSIONS

There is a slight statistically significant mean difference between the ECD values obtained from the 2 specular microscopes, which is negated by standardization to a single analysis method. Eye banks and surgeons should use caution in making decisions based only on very small differences in ECD between otherwise equivalent corneal donor tissues.

Representation of Central Endothelial Cell Density by Analysis of Single Best Specular Microscopy Image Regardless of Cell Size Variance

Purpose

The purpose of this study is to evaluate whether a single best image can represent central endothelial cell density (ECD) in corneas of differing cell size coefficient of variance (CV).

Methods

Four hundred one healthy eyes but with variant CV values were enrolled. For each eye, three nonoverlapping central cornea endothelium images were obtained with Konan NSP-9900 specular microscope. ECD and CV were evaluated by two independent graders using the well-established Center method. Only corneas with high image quality rating (IQR) and ECD >800 cell/mm² by both graders were included in the study. The study sample was stratified into five CV levels (CV ≤ 35; ≥36; ≥38; ≥40; and ≥45). In each CV level, the ECD agreement, ECD variance, and the correlation between the ECD variation and CV values were analyzed. In addition, the ECD intragrader reproducibility and interframe differences were also analyzed for all levels except CV ≤ 35.

Results

The study sample includes a total of 278 eyes. High ECD agreement for the two independent graders (intraclass correlation coefficient [ICC] > 0.99), high ECD intragrader reproducibility (ICC > 0.95), low ECD variance (2.0% ± 1.6%, overall), no correlation between the ECD variation and the CV value (P > 0.05), and no significant ECD difference among frames (P > 0.05) was found in any studied CV levels.

Conclusions

CV does not appear to be associated with ECD variance in the central cornea.

Translational Relevance

This finding highlights that in healthy corneas but with high CV values, ECD can be reliably analyzed using one single image of best quality.