The "marche-en-étoile" revised. The influence of after-images and prism-glasses on starwalks.

An analysis of the role that casual after-images play in starwalk (marche-en-étoile) tests, shows that these can be turned from unreliable into reliable tests. The vestibular function test described in this article is as follows: (a) the individual walks with open eyes to a point of reference 5 m distant. On arrival, he closes his eyes and walks backward and forward according to the marche-en-étoile procedure. (b) Same procedure as (a), but now the orientation point is replaced by a light source that is switched off when the patient reaches it. (c) Same procedure as (b), but now the patient is wearing prism-glasses. It turns out, the deviations in the starwalk are caused mainly by drifting of the after-image. This drift is based on an oculogyral illusion, and it appears that it can be influenced by wearing prism-glasses. These investigations reveal the existence of hitherto too little known interactions between the vestibular and the visual system.