Using motion perimetry to detect visual field defects in patients with idiopathic intracranial hypertension

Abstract

Motion perimetry, a method of visual field testing that uses computer graphics to measure motion perception, quantitates a subject's ability to detect a coherent shift in position of dots in a defined circular area against a background of fixed dots. Motion size threshold is defined as the smallest detectable circular target in which dot motion is detected. Subjects respond by touching a computer monitor screen with a light pen, first when they see a target (reaction time) and a second time where motion targets are detected (localization). Reaction time (msec) to the stimulus and localization error (number of pixels from target center) are then calculated and stored. We tested on eye in each of 20 idiopathic intracranial hypertension (IIH) patients and 40 age-matched normal subjects by conventional automated perimetry (Humphrey visual field analyzer, program 24-2) and motion perimetry. Pointwise probability plots of individual abnormal test points for size threshold responses were generated for the IIH patients based on the 95% confidence limits of the normal subject responses. An analysis of the subjects' visual field pairs (motion versus conventional automated perimetry) was performed based on these probability plots. The IIH patients had an elevated mean motion threshold (p < 0.001) and reaction time (p < 0.001) compared with the normal subjects. There were no significant differences for the localization errors. Based on the probability plot analysis, there was good correlation of the visual field defects between the two perimetry tests. In addition, motion perimetry identified nerve fiber bundle-shaped defects in nine patients in whom they were not detected with conventional automated perimetry.