An instrument similar to the Hess screen. It consists of two internally illuminated screens placed at right angles. One eye views one screen directly, the other views the second screen via a mirror; hence, the eyes are dissociated. When one eye fixates a point on one illuminated screen, its position as seen by the second eye is indicated with a wand on the second, non-illuminated screen. When this is illuminated, the position of the wand relative to the screen markings indicates whether a muscle or set of muscles is paretic or not.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann