Normal tension glaucoma (NTG) is almost the most difficult type of glaucoma to diagnose.The difficulty lies in the lack of specificity of the symptoms and signs of glaucomatous optic neuropathy (GON), so the reevaluation of NTG is a new understanding of GON.As a subtype of primary open-angle glaucoma (POAG), NTG is difficult to accurately conceptualize.One of the reasons is that the intraocular pressure (IOP) is closely linked to the occurrence of GON in POAG but not in NTG.GON seems to be secondary to a number of local or systemic disorders, including vascular dysfunction in the optic nerve head induced by compression (elevated IOP) or ischemia, hypoxia, migraine, Flammer syndrome, intracranial hypotension, low body mass index, low estrogen levels, nocturnal hypotension, obstructive sleep apnea-hypopnea syndrome, Alzheimer disease, Parkinson disease, and genetic background, which may influence the flow in the radial peripapillary capillaries (RPCs) and the underfilling of RPCs causing retinal ganglion cell damage.In some cases, GON does not progress with systemic diseases under control, and these systemic diseases are not risk factors for NTG but may be the cause of GON (or GON is one of the manifestations of these diseases). If these causes are not excluded and NTG is diagnosed only on the basis of GON, chamber angle opening, and normal IOP, it is easy to cause misdiagnosis, and the complete exclusion of these diseases is short of clinical significance in practice.In conclusion, the diagnosis of NTG may not be made before the other ocular or systemic disorders capable of presenting with GON are ruled out, and the concept and diagnostic criteria of NTG should be reconsidered.