Functional visual field loss is traditionally assessed by kinetic perimetry, typically producing spiralling isopters. This study looked at the spatial distributions of functional field deficits using automated static perimetry. A retrospective review of automated perimetry records was conducted using a database to identify participants diagnosed with functional visual field loss. Thirty-six cases were found meeting the clinical and tangent screen criteria for functional visual field loss. Thirty-three normal eyes and 57 eyes with true lesions, including optic nerve compression, glaucoma, anterior ischaemic optic neuropathy and vigabatrin toxicity, served as controls. Perimetry consisted of high-pass resolution perimetry using vanishing resolution targets at 50 test locations inside 30 degree eccentricity. The results of standard automated perimetry statistics were unable to reliably discriminate organic versus non-organic visual field loss. Subjective evaluation of visual field results showed that functional fields generally could be identified by the presence of severe and irregular contractions and depressions as well as one or more isolated threshold ‘spikes’, that is, isolated locations showing much better than average sensitivity. On repeated examinations functional field loss was variable between examinations. In the absence of kinetic perimetry, functional visual loss can be identified by automated static perimetry. Useful criteria include severe and irregular contractions and depressions, the presence of isolated threshold spikes and poor inter-test correlations. 

Identification of functional visual field loss by automated static perimetry.
Frisen L.
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Nana Theodorou

BMedSCi (Hons) PhD, Sheffield Teaching Hospitals NHS Foundation Trust, Clinical Research Office, 11 Broomfield Road, Sheffield, S10 2SE, UK.

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