Normal pressure glaucoma (or normal tension glaucoma) is an optic neuropathy associated with low intraocular pressure (ie less than 22 mmHg).

The following are known associations of normal pressure glaucoma:
• steroid use (eg nasal sprays, inhaled or oral steroids, or steroid creams) - in this case steroids may infact elevate IOP but this may not be detected and be falsely diagnosed as normal pressure glaucoma
• vasospasm – migraine / Raynauds
• coagulopathies – previous blood loss or shock like epsiode
• systemic nocturnal hypotension
• autoimmune disease
• thyroid disease (increased risk)
• sleep apnoea (especially in overweight men)
• Alzheimer's disease

Other problems to be considered
• intermittent IOP elevation - can be excluded with diurnal IOP measurements
• burnt out glaucoma
• congenital anomaly
• myopia with peri-papillary atrophy
• optic nerve coloboma
• vascular etiology
• carotid occlusion
• previous blood loss
• hereditary optic neuropathy
• Lebers optic neuropathy
• tonometric error (thin cornea)

Investigations
• FBC – rule out anaemia
• CRP / ESR – rule out a condition called "anterior ischaemic optic neuropathy"
• VDRL/FTA – syphilis is a very rare association
• ANA – autoimmune diseases, also Ro, La, Sm
• paraproteinaemia – rule out lymphoproliferative disease
• Lebers – mitochondrial testing where indicated

Imaging
• HRT / OCT / GDx
• MRI if asymmetry, unusual VF, progressive fields, dyschromatopsia, APD with mild cupping
• carotid dopplers
• CXR to rule out sarcoidosis

Other tests
• 24 hour ambulatory blood pressure monitoring

Treatment
• ALT not recommended
• Trabeculectomy with Mitomycin C, if IOP in single digits is required
• In some cases, your physician might recommend Ginkgo Biloba (40mg three times a day). There is some evidence that points to a benefit here, but this medication is not suitable for everyone and it's use is advised on a case-by-case basis, after discussion with your glaucoma specialist.
• Future medication, for selected subgroups of patients with glaucoma, may include memantine, a tablet medication that may have beneficial protective effects on the optic nerve (randomised controlled trials are awaited).

Ginkgo Biloba - not recommended for most patients with glaucoma - little evidence for benefit.