Observation of head-shaking nystagmus with an infrared Frenzel's glass.

It has been reported that a head-shaking test is very useful in clinical practice. To observe head-shaking nystagmus (HSN) a Frenzel's glass and electronystagmography (ENG) have been used. Although observation with Frenzel's glass is a simple method, it tends to suppress after shaking nystagmus, as gazing is not completely eliminated with Frenzel's glass. An electronystagmogram in darkness can eliminate gazing completely, but it requires much trouble in routine use. We therefore tried to use Frenzel's glass with an infrared CCD camera. We observed highly provoked HSN like ENG in darkness and were able to use it without difficulty. We recognized the second phase in several cases with only an infrared Frenzel's glass and the rotatory component of the nystagmus. This method is more convenient and valuable for clinical use than ENG and Frenzel's glass.