This is type of open angle glaucoma with wide open angle by gonioscopy and the intraocular pressure is normal range but there is progressive visual field defects and progressive glaucomatous optic disc cupping with the absence of secondary causes for optic disc damage.
One possible mechanism of this glaucoma is vascular insufficiency to the optic nerve which makes the disc less resistance and more vulnerable to be damaged by normal intraocular pressure. Sometimes the intraocular pressure is even lower than normal and that is why it is also called low pressure glaucoma.
This type of glaucoma occurs in old age with female gender at risk more than male. Also it occurs more frequently in Japan. Family history is also considered as a risk factor
There are systemic associations with this type of glaucoma which will help to define the diagnosis like hypertension, peripheral vascular spasm which is called Raynaud phenomena and migraine.
Nocturnal hypotension that occurs during sleep, is one of the factor that cause this disease.
Treatment of this condition is by antiglaucoma medications to lower the intraocular pressure to a level in which there is no further damage to the optic nerve. There should be regular followup to make sure that the visual field test and OCT are stable with no progressive damage to optic disc. Treatment also can be done by surgical treatment in case medical treatment failed.
Also we should treat the nocturnal hypotension that occurs during sleep which play a rule in the pathogenesis of the disease