title: A bedside test to determine motion stereopsis using the Pulfrich phenomenon.
abstract: OBJECTIVE
  Many diseases induce asymmetric delays in the visual pathway, resulting in a spontaneous Pulfrich phenomenon (PP). The PP is a visual stereoillusion that may cause difficulties in persons when traveling in cars, crossing the road, or playing ball games. The authors developed and tested a simple new bedside procedure to detect PP.
  
  
  METHODS
  A case series.
  
  
  METHODS
  Disease simulation in 2 normal subjects and 18 patients with optic neuritis (ON) was examined. Ninety normal subjects were studied to determine normal range of PP.
  
  
  METHODS
  The new test, called swinging pen test (SPT), is performed by oscillating a pen by hand. The SPT was compared to a gold standard, a mechanical pendulum (MP).
  
  
  METHODS
  The authors measured simulated PP in two normal subjects and PP in 18 patients with ON and 90 normal control subjects. The Pearson product-moment correlation (r) and the Spearman rank correlation (rs) between SPT and MP were calculated.
  
  
  RESULTS
  The magnitudes of simulated PP determined with the SPT and the MP correlated well (r = 0.92, P < 0.005, and r = 0.96, P < 0.001). Correlation also was good in patients with ON (rs = 0.90, P < 0.05). The positive predictive value of the SPT was 100%, and the negative predictive value was 92%. The PP was absent in all control subjects testing with either pendulum. The normal range for PP varied from -1.40 to 1.52 msec. For the SPT, the intraobserver variability coefficient was 8.2%, and the interobserver variability coefficient was 10.5%.
  
  
  CONCLUSIONS
  The authors believe that SPT will be of value to clinicians on bedside evaluation of motion stereopsis dysfunctions. The normal range of PP was approximately +/- -1.5 msec (approximately +/- -1.5 cm), corresponding to a 0.3-log unit neutral density filter).
authors.affiliation: Department of Ophthalmology, University of Bern, Switzerland.
authors.forename: D S
authors.initials: DS
authors.lastname: Mojon
authors.forename: K M
authors.initials: KM
authors.lastname: Rösler
authors.forename: H
authors.initials: H
authors.lastname: Oetliker
mesh_terms: D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D003867:Depth Perception; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D007088:Illusions; D008297:Male; D008875:Middle Aged; D009039:Motion Perception; D009902:Optic Neuritis / Q000150:complications / Q000503:physiopathology; D010468:Perceptual Disorders / Q000175:diagnosis* / Q000503:physiopathology; D010469:Perceptual Distortion; D019095:Point-of-Care Systems; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014795:Visual Pathways / Q000503:physiopathology