Visual latency in the spontaneous Pulfrich effect

Abstract

Background. Interocular visual latency differences in patients with traumatic optic neuropathy due to midface injury were compared using both measurements of the delay from the spontaneous Pulfrich effect and pattern visual evoked potentials (VEPs).

Methods. Six patients with a spontaneous Pulfrich effect following midfacial injury observed a target which oscillated sinusoidally with an elliptical path in the frontal plane. The spontaneous Pulfrich delay was calculated from the size of the minor axis of the target ellipse on an XY plotter adjusted until the patient judged that no depth (i.e. no ellipse) was seen. Six separate pattern-reversal VEPs were recorded monocularly, with an artificial pupil, for a 4 cycle/degree grating. The mean P100 peak latency for each eye was used to calculate interocular latency differences. For both the Pulfrich effect and VEP measures normal subjects were included for comparison.

Results. Patients had P100 delays ranging from 2.8 to 17.8 ms, whereas Pulfrich delays were much shorter, ranging from 0.14 to 1.3 ms. A significant positive correlation was found between the two measures of delay, but the magnitude of the interocular difference in VEP was much greater than the delay calculated for the spontaneous Pulfrich effect. Tints used to correct the spontaneous Pulfrich effect in the patients were generally of high transmission (75–85%) and not dense enough to provoke an effect in normal observers.

Conclusion. We have described a technique to quantify interocular delay associated with a spontaneous Pulfrich effect in patients with midfacial trauma. Interocular delays measured from pattern-reversal VEPs are similar in direction and relative severity but are larger in absolute terms.