Adopting Popper's points of view on objective knowledge towards the theory that increased intraocular pressure is the cause of optic nerve atrophy in chronic glaucoma, we find numerous attempts to support this theory by ad hoc hypotheses. This occurs at the cost of diminished prediction value. Preliminary investigations aiming at a verification of the beneficent effect of pressure reduction in glaucoma by applying improved methods have given disappointing results. Prospective, randomized studies on groups of treated and nontreated patients with manifest glaucoma are necessary in order to falsify or verify the pressure theory.