Reproducibility and reliability of central corneal thickness determination in more and less profound corneal edema using ultrasound pachymetry, a Scheimpflug camera and anterior segment OCT.

PURPOSE

The purpose of this study is to determine the influence of different degrees of corneal edema on the reliability and reproducibility of central corneal thickness(CCT) measurements by a Scheimpflug camera (Pentacam), anterior segment optical coherence tomography(AS-OCT) and ultrasound pachymetry(USP).

METHODS

Forty-four patients undergoing ophthalmic surgery were included in this prospective study. All measurements were acquired by two investigators. The Pentacam and AS-OCT measurements were performed in randomized order followed by USP. Two measurements were taken by each investigator with each device. CCT was evaluated by using the apex value provided by the Pentacam, the corneal apex cut in the AS-OCT and averaging 2 cycles of 4 measurements for USP. Coefficients of variation (COV) and intraclass correlation coefficients (ICC) were determined. To investigate the reproducibility in different degrees of corneal edema, patients were subdivided into edema more/less than 10% of CCT, ≥/< 600 μm and > 650 μm CCT.

RESULTS

No significant differences were recorded for each individual investigator and measuring device. However, overall the devices differed significantly in the < 600 μm group (ANOVA p < 0.04). The reproducibility decreased with higher degrees of corneal edema in particular for investigator 1 and USP measurements. No significant overestimation of corneal thickness by the Pentacam was recorded in higher degrees of corneal edema.

CONCLUSION

USP measurements are highly user dependent especially in higher degrees of corneal edema. Nevertheless, all methods were able to reach a high level of agreement in CCT measurement in higher degrees of corneal edema. Interestingly lower degrees of corneal edema revealed the only significant differences in-between the 3 devices.