Nystagmus are best viewed using infrared videonystagmography, however, other techniques can partially reduce visual fixation known to suppress vestibular nystagmus. Alternative viewing techniques include Frenzel’s glasses or direct observation assisted by a penlight, otoscope, or ophthalmoscope.
Guidetti, Monzani, and Rovatti (2006) compared three observation techniques (direct visual observation, Frenzel’s glasses and infra-red assisted videonystagmography) used in the examination of patients with suspected vestibular dysfunction, specifically patients with a history of vertigo, asymptomatic at the time of examination. Each patient was examined for possible spontaneous, positional and head-shake nystagmus. Videonystagmography was able to discriminate between patients with vestibular dysfunction versus normal controls with 78% accuracy. The discriminant power of Frenzel’s glasses was 52%, while direct observation was able to correctly identify vestibular patients versus normal controls with only 46% accuracy. The authors suspected that direct observation and Frenzel’s glasses were less accurate due to their inability to totally remove visual fixation. Additionally, videonystagmography allows for an enlarged view of the eye on a TV or computer monitor, and allows playback for review or consultation.
In patients with acute vertigo at the time of examination (which was the topic of the previous five part series), inspection for spontaneous nystagmus is a crucial and simple method to reliably separate those with central from peripheral pathology.
In a sample of 100 patients presenting with acute vertigo and spontaneous nystagmus (all identified by videonystagmography), only 33 had visible nystagmus when viewed under Frenzel’s glasses (Baba et al., 2004).
So, you have to ask yourself, “Since the vast majority of patients with acute vertigo are peripheral, and this can easily be determined if you can accurately and sensitively view the nystagmus pattern, why in the world is there not a set of infra-red videonystagmography goggles in every emergency room in the country?”
Baba, S., Fukumonto, A., Aoyagi, M., Koizumi, Y., Ikezono, T., & Yagi, T. (2004). A comparative study on the observation of spontaneous nystagmus with frenzel glasses and an infrared CCD camera. J Nippon Med Sch, 71(1), 25-29.
Guidetti, G., Monzani, D., & Rovatti, V. (2006). Clinical examination of labyrinthine-defective patients out of the vertigo attack: sensitivity and specificity of three low-cost methods. Acta Otorhinolaryngol Ital, 26, 96-101.