The problem of glaucoma as a cause of blindness is discussed. WHO has proposed five classes of sightlessness on the sole basis of visual acuity without taking into account sense of luminosity, peripheral vision, color vision. In addition, different nations have different tables for evaluating the severity of the handicap so that data on this subject cannot be compared. This is why the problem of blindness due to glaucoma is very complicated and the concept of blindness has to be standardized as well as the method of epidemiologic research. The investigation starts from a list of the most reliable sources: records of associations of sightless subjects, lists of sightless persons receiving an invalidity pension, filed research, records of support activities and transversal population studies. This is followed by a general review of causes of blindness worldwide, their prevalence according to age and sex, and especially the causes of blindness in various nations and in different regions of Italy. Last, the percentage of loss of eye-sight due to glaucoma is examined.