Comparison of Corneal Thickness Measurements using Ultrasound Pachymetry, Ultrasound Biomicroscopy, and Digital Caliper in Frozen Canine Corneas

Abstract

ABSTRACT The purpose of this study was to evaluate the clinical efficacy among ultrasound pachymetry (UP), ultrasound biomicroscopy (UBM), and manual measurement (MM) with digital caliper by comparing corneal thickness (COT) values obtained on frozen canine corneas ex vivo. The COT was measured using UP, UBM, and MM in 8 enucleated normal canine eyes frozen at -20℃ for 4 weeks. After thawing at room temperature for 2 hrs, the COT values were obtained from five sites of each cornea: central corneal thickness (CCOT), thickness at the 3, 6, 9, and 12 oclock positions (3COT, 6COT, 9COT, and 12COT, respectively). For each device, measurements were performed three times at each designated site by one operator. Intraclass correlation coefficient, one-way analysis of variance, and Bland-Altman plot were performed for statistical analyses. The mean CCOT was 839.0 ± 138.2 μm, 857.6 ± 127.9 μm, and 849.1 ± 132.8 μm for UP, UBM, and MM, respectively. There was no statistically significant difference among the measurements by all three devices. The statistical agreement among these devices was also shown to be good according to Bland-Altman plots. In addition, the values measured on the peripheral sites of the cornea (3COT, 6COT, 9COT, and 12COT) also revealed no significant differences among the three devices. The difference between CCOT and peripheral corneal thickness (PCOT) was also statistically insignificant. Based on the results of the present study, the UP, UBM, and MM measurements showed statistically similar COT values. The UBM and UP provided accurate and reliable measurements comparable to MM, and could be used effectively for clinical COT measurements