Why does the world look like it's moving when it's not, in people with some types of nystagmus?

Overview

Nystagmus is the name for repetitive and involuntary eye movements. It can affect vision badly by giving the feeling that world is moving when it’s not. This is an unpleasant sensation called oscillopsia.

Normally, the brain ‘subtracts’ eye movements from any movement in the outside world, so that the visual scene is still. But the system isn’t perfect. If certain eye movements aren’t completely cancelled out by motion in the world, we can experience an illusion of background motion. The Filhene illusion, as its known, can be used to measure how accurately the visual system is at compensating for eye movements.

Nystagmus doesn’t always lead to oscillopsia. Previous research suggests that people who’ve had nystagmus since birth (infantile nystagmus syndrome) don’t experience it, but people can be badly affected if they develop nystagmus, for example due to a stroke.

In this study, the research team wants to find out about what causes the experience of oscillopsia. They are using eye-tracking and a version of the Filhene illusion to find out how well eye movements are cancelled out in people with infantile or acquired nystagmus and in people with normal vision. The aim is to use the results to help develop a therapy to reduce oscillopsia.