Do Frenzel glasses have a place in the modern electronystagmography laboratory?

Electronystagmography (ENG) is generally performed with the patient's eyes closed to prevent visual fixation. In this way, direct observation of eye movements is impossible. By means of Frenzel glasses (FG), the direct observation of eye movements is possible, but the effectiveness of visual fixation suppression and the diagnostic contribution of FG must still be studied. One hundred seven patients with vertigo participated in this study. Each patient underwent a complete ENG test under two fixation modalities: (a) closed eyes and (b) open eyes with FG. The spontaneous nystagmus and the Hallpike test did not show any significant difference between the two fixation modalities. The slow-phase velocity of nystagmus with the caloric test was significantly greater with closed eyes, but the pattern of nystagmus with FG fixation was more tooth-shaped and regular than that with closed eyes. It is concluded that using FG when performing an ENG may improve its diagnostic value.