Normal tension glaucoma (NTG) is considered a primary optic neuropathy within the glaucoma family. Whereas NTG shares many of the same pathologic characteristics as primary open angle glaucoma (POAG), there are several differences such as pattern of visual field defect and incidence of disc hemorrhaging. The most notable difference is that NTG does not manifest a recordable intraocular pressure (IOP) greater than 21 mmHg. Debate has existed as to whether NTG is a pressure-sensitive neuropathy and if pressure reduction affects the course of the disease. Likely, there are aspects in the pathophysiology of NTG that are both pressure sensitive and insensitive, and the etiology of NTG has never been adequately explained.