Comparison Between Laser Scanning In Vivo Confocal Microscopy and Noncontact Specular Microscopy in Assessing Corneal Endothelial Cell Density and Central Corneal Thickness

Purpose: To compare central corneal thickness (CCT) and endothelial cell density (ECD) with laser scanning confocal microscope Heidelberg Retina Tomograph (HRT) II Rostock Corneal Module and noncontact specular microscope Tomey EM-3000 and to assess intra- and interobserver agreement in normal corneas. Methods: This prospective study included 48 normals (69.6 ± 7.2 years, range: 55-80 years) who underwent CCT and ECD with both Tomey and HRT 3 times by 2 independent observers. Measurement differences between instruments, agreement between devices, and test-retest variability (TRV) were determined. Results: Mean CCTs with Tomey and HRT were 529.4 ± 35.4 and 536 ± 37.6 μm (P = 0.06), respectively; average ECDs with Tomey and HRT were 2473.5 ± 242.2 and 2539.7 ± 338.6 cells per square millimeter (P = 0.04), respectively. The mean of the differences (HRT minus Tomey) was 6.5 ± 17 μm for CCT and 65 ± 135.1 cells per square millimeter for ECD. Differences between instruments were not related to CCT (P = 0.35), whereas significantly increased with increasing ECD (P = 0.0001). Intraexaminer TRV for Tomey and HRT were 3.9 ± 3.7 and 22.2 ± 18.4 μm for CCT and 73 ± 63.4 and 152.2 ± 148.4 cells per square millimeter for ECD, respectively; interexaminer TRV was 4.6 ± 4.2 and 23.8 ± 17.3 μm for CCT and 84.9 ± 72.3 and 159.8 ± 149.8 cells per square millimeter for ECD. Conclusions: HRT II Rostock Corneal Module and the Tomey EM-3000 showed an overall good intermethod agreement. HRT showed a tendency to slightly overestimate CCT measurements, significantly underestimate ECD measurements in eyes with a reduced cell density (<2290 cells per square millimeter), and overestimate ECD in eyes with a high cell density. Both instruments showed low intra- and interobserver TRV for both CCT and ECD measurements, which tended to be less for Tomey.

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