In a prospective study we measure the intra-ocular pressure (IOP) by means of a pneumotonometer and the central corneal thickness (CCT) in 245 healthy emmetropic or ametropic eyes consulting in a private practice. There is a linear relation between IOP measurement and CCT. The same measurements are done in 30 glaucomatous eyes and in 16 eyes with ocular hypertension. The mean CCT is similar in normal and glaucomatous eyes (554 mu). In eyes with ocular hypertension there is a manifest elevated CCT.