Normal tension glaucoma—a practical approach

[...]the level at which intraocular pressure (IOP) becomes abnormal has been a source of conjecture in the ophthalmic literature and the pros and cons of setting an arbitrary limit for use in the definition of NTG have been discussed elsewhere. 1 To try and simplify the issue we have included the following criteria for the definition of NTG as used in our clinic at Moorfields: A mean IOP off treatment consistently equal to or less than 21 mm Hg on diurnal testing, with no single measurement greater than 24 mm Hg Open drainage angles on gonioscopy Absence of any secondary cause for a glaucomatous optic neuropathy-for example, a previously raised IOP following trauma, a period of steroid administration, or an episode of uveitis Typical optic disc damage with glaucomatous cupping and loss of neuroretinal rim Visual field defect compatible with the glaucomatous cupping (disc/field correlation) Progression of glaucomatous damage. [...]the progressive nature of the disease should always be borne in mind as this will help to distinguish true NTG from an isolated ischaemic event which may mimic it in terms of optic disc and visual field appearances. 4 Epidemiology There are around 150 000 patients in the UK with diagnosed glaucoma and the same number again with undiagnosed disease. 5 One third of the patients with POAG can be classified as having NTG. 6 7 Bearing in mind that glaucoma is currently the second commonest cause of blindness worldwide, and it is estimated that by the year 2000 it will be the commonest cause of untreatable blindness, 8 the prevalence of NTG faces us with a substantial problem.