Computer-based test to quantify the Pulfrich stereophenomenon.

Background: Many eye and brain diseases may induce a spontaneous Pulfrich phenomenon (PP), a stereoillusion leading to misjudgments of objects moving in a frontoparallel plane. Since, until now, no simple PP quantification method has been available, a computer pendulum (CP) system was developed and evaluated.

Methods: In 5 normal subjects, PP was induced with different neutral density filters. The resulting retardations were measured with the gold standard (a mechanical pendulum; MP), and compared to a CP, allowing the generation of interocular image phase shifts.

Results: A high correlation between MP and CP was found (r = 0.97, p < 0.001; slope 0.91, p > 0.1 for difference with slope 1.0). A multiple linear regression showed a significant influence of the filter density and the subject tested. The type of pendulum (MP or CP) and the side on which the filter was held were nonsignificant.

Conclusions: A CP allowing an interocular image phase shift can be used as an alternative to a MP for quantification of a PP. Thus, this principle would allow the development of software or an Internet-based test for PP quantification. However, in some subjects, the CP will overestimate and in others underestimate the real retardation measured with the MP.