The reliability of central corneal thickness measurements by ultrasound and by Orbscan system in schoolchildren.

PURPOSE

To compare the central corneal thickness measurements obtained by ultrasound (US) pachymetry and the Orbscan II system in healthy schoolchildren.

METHODS

A total of 356 schoolchildren aged 7 to 12 years underwent central cornal thickness (CCT) measurement with Orbscan II and ultrasonic pachymetry. All eyes were examined first with the Orbscan II and then by US pachymetry. The mean of the difference, standard deviation (SD), and 95% limits of agreement, with and without applying the acoustic correction factor, were determined. The differences between the devices in measuring mean CCT were calculated with paired-sample t test. Pearson correlation test was used to determine the correlation between variables. p < 0.05 was considered to be statistically significant. Linear regression analysis was used to quantify the correlation between the two methods.

RESULTS

Orbscan II measurements were significantly higher than US pachymetry measurements without applying the manufacturer-recommended acoustic correction factor (0.92) correction (580.39 +/- 37 microm and 562.95 +/- 32 microm, respectively) (p < 0.0001). When this acoustic correction factor was applied, the Orbscan II measurements demonstrated significantly lower results when compared with those of US pachymetry (533.96 +/- 34 microm and 562.95 +/- 32 microm, respectively) (p < 0.0001). The linear regression analysis lines showed approximately 45-degree slope indicating a strong correlation between these methods (US pachymetry = 145.71 + 0.72 x Orbscan II value without acoustic correction factor (microm), r = 0.89, p < 0.0001). There was a high degree of variability in differences between the 2 devices in individual subjects. The range was between 25 to -55 microm without the acoustic correction factor and 67 to -5 microm with the acoustic correction factor.

CONCLUSIONS

Although US pachymetry and Orbscan II demonstrated a strong linear correlation, there was a high degree of variability in differences between the two devices in individual subjects who participated.