The reliability of Frenzel's glasses and the optimal observation period for routine explorations

In many clinics and medical offices the electrographical registrations of vestibular reactions are only available for patients with special problems. For routine explorations Frenzel's glasses are still in use. It was one purpose of our studies to show that the observation with Frenzel's glasses is no less effective than ENG registration, in regard to nystagmus frequency. This result is based on investigations with special equipment for simultaneous registration and computerized evaluations. The disadvantage using Frenzel's glasses without any other equipment is the impossibility of determining the culmination phase exactly. Therefore we looked for a defined period in which the frequency was correlated best to the frequency of the culmination phase determined by ENG recordings. A total of more than 100 different intervals were analyzed. The optimal period for routine investigations is a 1 min interval beginning 10 sec after the end of irrigation. Limiting the evaluation of a caloric response to this defined observation period is recommended for various reasons.