Glaucoma in the far-sighted, who have smaller-than-normal anterior chambers, making physical contact between the iris and trabecular meshwork more likely. Normal-tension glaucoma (also "NTG", "low-tension glaucoma", "normal-pressure glaucoma") is a condition where the optic nerve is damaged although intraocular pressure (IOP) is in the normal range (12-22mm Hg). Individuals with a family history of NTG, those of Japanese ancestry, and those with a history of systemic heart disease are at higher than average risk of developing NTG. The cause of NTG is unknown. Secondary glaucoma refers to any case in which another disease, trauma, drug or procedure causes increased eye pressure,
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