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Quantitative imaging of the optic nerve head has become a pillar in glaucoma diagnosis. Several technologies and devices have been used such as confocal laser scanning tomography, optical coherence tomography and 'simple' fundus photography. Since patients may move or ophthalmologists may change their preferred technique, the question arises how much results of the different methods are interchangeable. Barkana et al. (667), therefore, compared the optic disc measurements obtained with these three methods and found strong evidence of a large range of differences between the methods. It clearly shows that optic nerve had measurements obtained with different techniques are not interchangeable in clinical practice. In addition, a poor agreement between these methods in classifying small discs, medium sized discs, and large discs was found so that the estimation of the absolute disc size and the estimation of the relative disk size may only be defined separately for each technique. These results are important for the clinical routine in glaucoma.