A single tonometry observation is not very relevant due to considerable interobserver variations which are also found in applanation tonometry. Furthermore, the intraocular decreases by repeated applanation tonometry and intra-ocular pressure that change for as much as 8 mm Hg in 1 minute has been found in continous pressure recordings. There are in addition diurnal pressure variations and pressure alterations with the position of the body. Therefore, the diurnal pressure curve is much more important than the single tonometric value. The prognosis and also the decision to start medical treatment depends upon the height of the pressure, the family history diabetes, vasoclerosis, low blood pressure, heart insufficiency, age, disease of the carotid artery, anemia, the size of the excavation, the condition of the visual field, the reliability of the patient and the pressure lowering effects of pilocarpine, which can be very different individually. Rarely pressures of 26 mm Hg or more can be left untreated. If unfavourable factors are combined, even in pressures of 20 mm Hg it should be tested if pilocarpin lowers the intra-ocular pressure considerably. There is no magic number of pressure where treatment has to be started.