A BEDSIDE TEST TO DETERMINE MOTION STEREOPSIS USING THE PULFRICH PHENOMENON

Objective: Many diseases induce asymmetric delays in the visual pathwa y, resulting in a spontaneous Pulfrich phenomenon (PP), The PP is a vi sual stereoillusion that may cause difficulties in persons when travel ing in cars, crossing the road, or playing ball games. The authors dev eloped and tested a simple new bedside procedure to detect PP. Design: A case series. Participants: Disease simulation in 2 normal subjects and 18 patients with optic neuritis (ON) was examined. Ninety normal s ubjects were studied to determine normal range of PP. Intervention: Th e new test, called swinging pen test (SPT), is performed by oscillatin g a pen by hand. The SPT was compared to a gold standard, a mechanical pendulum (MP). Main Outcome Measures: 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 S pearman rank correlation (r(s)) between SPT and MP were calculated. Re sults: 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), Cor relation also was good in patients with ON (r(s) = 0.90, P < 0.05). Th e positive predictive value of the SPT was 100%, and the negative pred ictive value was 92%, The PP was absent in all control subjects testin g 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%. Conclusi ons: The authors believe that SPT will be of value to clinicians on be dside evaluation of motion stereopsis dysfunctions, The normal range o f PP was approximately +/- -1.5 msec (approximately +/- -1,5 cm), corr esponding to a 0.3-log unit neutral density filter).