The Pulfrich stereo-illusion as an index of optic nerve dysfunction.

A simple test based on the Pulfrich phenomenon may provide an indication of optic nerve dysfunction. When a small object swinging pendulum fashion is viewed binocularly by a person with one eye covered by a neutral density filter, the object appears to swing in an elliptical path. The patient with optic nerve dysfunction may see it this way without use of a filter. The Pulfrich theory is explained, clinical applications are discussed, and instructions for constructing a Pulfrich apparatus are given.