“…(4) Until 1955, there were no standardized tonometer in Europe. (2) Since Leydhecker's investigations, it has been known that there is an interval of around 5 to 10 years between early detection of POAG and the first signs of optic neuropathy (pre-perimetric Glaucoma) or, even later, of functional changes. (5) This interval represents the resistance of the optic nerve to ocular hypertension (OH).…”