Patients with glaucoma and those suspected of having glaucoma comprise an approximate 30% of follow-up outpatient visits and 15% of new-patient assessment visits within the Hospital Eye Service (HES). This figure seems likely to increase in line with the demographic trends in the population and as optometrists improve their detection of the glaucomas, including primary open-angle glaucoma (POAG). 

Epidemiological studies suggest that, in developed countries, about 50% of glaucoma patients have had their disease detected (ie about one-half of all cases remain undetected). For example, in the Rotterdam Study, 52.9% of the patients found to have POAG were not previously diagnosed (Dielemans et al. 1994). Patients with POAG are typically asymptomatic until significant visual loss has occurred, and this insidious nature of presentation contributes to the low levels of detection.