Editor,—In their discussion on central corneal thickness determined with optical coherence tomography in glaucoma in the BJO, Bechmann et al 1 mention the results of Ehlerset al.2 and compare them with the results of Whitacre et al 3without regarding generally accepted principles of interpretation.4 Some biometrical considerations will be found in the following.

In the paper by Ehlers et al in figure 4 the correlation coefficient between the correction value and corneal thickness is 0.768 at n = 29. In the comparable figure 2 of Whitacreet al no correlation coefficient is given at n = 15. This coefficient was calculated by us after digitalising the data points. It equals 0.51. According …