Interocular Symmetry and Repeatability of Central Corneal Thickness and Corneal Endothelial Cell Morphology and Density in Healthy Eyes of Congolese

Purpose To determine the limits of normal interocular symmetry and the repeatability of central corneal thickness (CCT) and endothelial cell morphology and density. Methods Two hundred and seventy-eight subjects (age: 10.9-80.7 years) with healthy eyes were studied. CCT as well as endothelial cell morphology and density were measured by non-contact specular microscopy. Three measurements were obtained per eye per participant. Upper and lower tolerance limits of normal interocular symmetry were defined as the 2.5th and 97.5th percentiles of the interocular differences in CCT, endothelial cell density (CECD), coefficient of variation (CoV), hexagonality, and cell size. Repeatability was determined using the intraclass coefficient correlation (ICC), the coefficient of variation (CV), and the test-retest variability standard deviation (TRTSD). Results The mean interocular differences were -1.05 +/- 17.5 mu m (p = .32) for CCT and 0.5 +/- 90.8 cells/mm(2) (p = .76) for CECD. The 2.5th and 97.5th percentiles of the interocular differences were -13.9 and 15.4 mu m for CCT and -177.4 cells/mm(2) to 182.0 cells/mm(2) for CECD. Only interocular difference in CoV correlated weakly with age (r = -0.22, P < .001). ICCs were 0.93 (95% CI: 0.89-0.96, P < .001) for CCT and 0.95 (0.94-0.96, P < .001) for CECD. CV and TRTSD were 1.2% +/- 5.3% and 4.4 +/- 3.4 mu m for CCT and 2.4% +/- 3.9% and 17.7 +/- 7.7 cells/mm(2) for CECD, respectively. Conclusions CCT and CECD showed good repeatability and interocular symmetry in normal Congolese subjects. Absolute interocular differences in CCT and CECD exceeding 15.5 mu m and 182 cells/mm(2), respectively, should be considered suspicious and investigated. When comparing two intrasession measurements from the same eye, a difference of approximately 4.5 mu m in CCT and 18 cells/mm(2) or greater may be considered statistically significant.