Glaucoma and Greenland. Positive family history is a risk factor for glaucoma. The relative risk of having primary open-angle glaucoma (P.O.A.G.) is increased about two- to four-fold for people who have a sibling with glaucoma. Glaucoma, particularly primary open-angle glaucoma, is associated with mutations in several genes, including "MYOC, ASB10, WDR36, NTF4", "TBK1", and "RPGRIP1", although most cases of glaucoma do not involve these genetic mutations. Normal-tension glaucoma, which comprises one-third of POAG, is also associated with genetic mutations (including "OPA1" and "OPTN" genes). Various rare congenital/genetic eye malformations are associated with glaucoma. Occasionally, failure of the normal third-trimester gestational atrophy
Normal tension glaucoma of cases that have been reported in medical literature in the 1980s and 1990s who had the typical signs of glaucomatous damage, like optic nerve head excavation and thinning of the retinal nerve fiber layer, while these patients had an IOP that would generally have been regarded as "normal". It is now widely estimated that a larger percentage of patients with primary open-angle glaucoma (POAG) are suffering from normal tension glaucoma: probably half of all POAG patients in Europe and the majority of POAG patients in East Asia. Among Americans of Japanese descent, for instance, the prevalence of NTG is