To compare specular microscopy values obtained using the Perseus (CSO, Italy) and the Nidek CEM-530 (NIDEK Co., Ltd. Japan) specular microscopes. This prospective study used specular microscopy to examine sixty eyes from thirty healthy subjects (29.83 ± 9.41 years; range 18–79 years). This was done with both the Nidek CEM-530 and the Perseus on three occasions and results were evaluated by one independent observer. Measurement differences between instruments and agreement between devices were determined. The endothelial cell sample was larger with the Perseus than with the CEM-530 (235.92 ± 38.26 vs. 184.38 ± 43.88, respectively) with a statistically significant difference (P = 0.001). Mean endothelial cell density (ECD) with the Perseus and CEM-530 was 2692.75 ± 306.66 and 2556.47 ± 257.38 cells/mm 2 (P = 0.001), respectively; mean coefficient of variation (CV) was 33.43 ± 4.29 and 28.70 ± 3.82 (P = 0.001), respectively, and hexagonality 56.66 ± 6.19 % and 68.50 ± 3.64 (P = 0.001), respectively. The mean of the differences (Perseus minus CEM-530) for ECD was 136.27 ± 106.16 cells/mm 2 (95 % CI 108.85–163.70 cells/mm 2); 4.73 ± 2.70 % (95 % CI 4.03–5.41) in CV; and −11.83 ± 5.05 for percentage of hexagonal cells. Both instruments showed significant differences in the measurement of all cell forms, predominantly higher values were found with the Perseus vs the CEM-530, except 4-sided cells. Endothelial cell density, coefficient of variation, and percentage of hexagonal cells between the Perseus and CEM-530 differ statistically. This shows that these instruments should not be used interchangeably.
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