Primary open-angle glaucoma (POAG) is a group of multifactorial diseases that affects 1.5% of the population. If untreated, the disease leads to irreversible damage to the visual system. The clinical features of POAG are excavation of the optic disc and visual field defects, probably due to degeneration of retinal ganglion cells. Important risk factors for POAG are older age, elevated intraocular pressure, the presence of POAG in relatives, and still largely unknown molecular genetic factors. The clinical, genetic and pathological heterogeneity most likely reflects the complex heterogeneous situation at the molecular level. The three genes known to be involved in POAG (MYOC, CYP1B1 and OPTN) account for up to 18% of the POAG cases. These findings result in new possibilities for the presymptomatic molecular diagnosis of POAG.