It is till now not definitely clear whether normal- and high-tension glaucoma are different forms of the same disease and whether they have similar pathogenetic mechanisms. Spectral domain optical coherence tomography (SD-OCT) is supposed to objectively evaluate retinal nerve fiber layer (RNFL) thickness. The investigators propose a study to compare the RNFL in patients with normal- and high-tension-glaucoma. In order to exclude other possible differences,which could influence the results, only patients with similar structural optic nerve head damage in both groups will be compared.