Note on the value of Frenzel's glasses for the recognition and qualitative evaluation of spontaneous nystagmus.

Spontaneous nystagmus encountered in neuro-otological practice is nearly always a physical sign of high diagnostic importance. Its localizing value is largely determined by certain of its qualitative characteristics and these are best studied and evaluated by means of the electronystagmograph, but for reasons discussed this is not suitable for use in smaller clinics. For the recognition and qualitative analysis of spontaneous nystagmus the use of Frenzel's glasses used in complete darkness, as recommended by Frenzel himself, has been found to give very satisfactory results.