Pupil perimetry in the diagnosis of functional visual field loss

The diagnosis of functional visual loss-reduced visual performance in the absence of an organic cause-is usually made by exclusion. We conducted a pilot study to evaluate pupil perimetry in three patients (aged 14,43 and 50) with visual field loss presumed to be functional on clinical grounds and having no cause identified by visual electrophysiology or magnetic resonance imaging. A modified automated perimeter was used to examine visual and pupil responses to a light stimulus (size 1.7) presented at five locations in the visual field (fixation and in each of the four quadrants). In each patient, the pupil responses were normal in those test quadrants which showed apparent visual field loss. Pupil perimetry provides objective evidence for a diagnosis of functional visual field loss in selected patients and may circumvent the need for other investigations.