A device for the optical analysis, including two-dimensional, of a thread or yarn (F) fed to a textile machine, said device comprising at least one light emitter element (3, 4) and at least one receiver element (5), said emitter element (3, 4) generating a light signal which strikes said thread (F) before being sensed by the receiver element (5) which, based on this sensing, defines a characteristic of the thread (F) such as its movement or its stoppage, a dimensional defect or another dimensional characteristic, between said light emitter element (3, 4) and said receiver element (5), there being interposed light transparent means (6) which are encountered by the light signal after it has interacted with the thread (F), and which act as a thread guide.