An unusual presentation of optic neuritis and the Pulfrich phenomenon.

The Pulfrich effect (named after Carl Pulfrich) is a well described visual stereoillusion observed when a swinging pendulum bob is viewed through a neutral density filter in front of one eye. The Pulfrich effect can be demonstrated spontaneously (ie, without a neutral density filter) in patients with multiple sclerosis because of the delayed optic nerve conduction seen after unilateral optic neuritis in multiple sclerosis. Here, a Pulfrich effect is described in a man with subclinical multiple sclerosis who only became symptomatic when playing squash.