Update on Normal Tension Glaucoma

Normal tension glaucoma (NTG) is labelled when typical glaucomatous disc changes, visual field defects and open anterior chamber angles are associated with intraocular pressure (IOP) constantly below 21 mmHg. Chronic low vascular perfusion, Raynaud's phenomenon, migraine, nocturnal systemic hypotension and over-treated systemic hypertension are the main causes of normal tension glaucoma. Goldmann applanation tonometry, gonioscopy, slit lamp biomicroscopy, optical coherence tomography and visual field analysis are the main tools of investigation for the diagnosis of NTG. Management follows the same principles of treatment for other chronic glaucomas: To reduce IOP by a substantial amount, sufficient to prevent disabling visual loss. Treatment is generally aimed to lower IOP by 30% from pre-existing levels to 12-14 mmHg. Betaxolol, brimonidine, prostaglandin analogues, trabeculectomy (in refractory cases), systemic calcium channel blockers (such as nifedipine) and 24-hour monitoring of blood pressure are considered in the management of NTG. The present review summarises risk factors, causes, pathogenesis, diagnosis and management of NTG.