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Normal pressure glaucoma (NPG) has a prevalence of 0.6% within white populations and is thought to account for 20-30% of primary open angle glaucoma. 1-3 It is characterised by an intraocular pressure that is found to be within the normal range together with cupping of the optic nerve head and visual field loss of a nerve fibre layer type.
The presence of visual field loss that comes close to fixation, so called "threatened" or "split" fixation, is of concern when managing glaucoma patients. Previous studies have shown that high tension glaucoma (HTG) patients with visual field defects which involve the central 5° of the visual field are at greater risk of losing visual acuity. 4 5 Visual acuity loss has also been shown to be more likely in these patients in the presence of inadequately controlled intraocular pressure (IOP). 4
Differences in the type of visual field loss seen in NPG compared with HTG have been suggested by several investigators. 6-12 It has also been shown that in NPG both central visual field loss, involving the central 10° field, and more peripheral field loss are related to the level of IOP. 13 What has not been established is whether the proximity to fixation of visual field loss relates to the likelihood of disease progression and the likelihood of deterioration in central visual function in NPG.
The purpose of this study was to compare the frequency and site of visual field progression and changes in visual acuity in NPG patients with and without pre-existing visual field loss that comes close to fixation.
Materials and methods
The hospital records of all patients attending the NPG clinic at Moorfields Eye Hospital who had at least 5 years of follow up with at least 10 automated visual field tests were reviewed. All patients who satisfied the following criteria for NPG were included in the study.
NPG was defined as the presence of (1) glaucomatous cupping of the optic nerve head; (2) untreated mean phasing IOP no greater than 21 mm Hg and no single reading greater than 23 mmHg; (3) the presence in either eye of a minimum visual field defect as defined below.
For each eye the following patient data were collected: age; sex; mean phasing IOP;...