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The takeaway Frenzel goggles: a Fresnel-based device
Michael Strupp1, Carolin Fischer2, Lena Hanß2
1From the German Center for Vertigo and Balance Disorders (M.S., C.F., L.H., O.B.), Department of Neurology (M.S.), and Institute of Biometrics and Epidemiology (O.B.), University Hospital, Munich, Germany. Michael.Strupp@med.uni-muenchen.de.
Objective:
To develop and evaluate new thin and light glasses for the examination of patients with nystagmus and to compare them with Frenzel goggles.
Methods:
First, we designed new examination glasses: a Fresnel-based device with a short focal length that is not as heavy or bulky as Frenzel goggles. Second, visual-fixation suppression of postrotatory nystagmus with Frenzel goggles and the Fresnel-based device, the latter with 2 different magnifications (2- and 4-fold), was compared in 13 healthy subjects. Third, the intensity of the peripheral vestibular spontaneous nystagmus-in 6 patients with acute vestibular neuritis-with the Frenzel goggles and the Fresnel-based device with the 4-fold magnification was compared. Fourth, the visibility and clinical applicability were evaluated.
Results:
The Fresnel-based device weighs 6 g (dimensions 12 × 8 × 0.3 cm). There was no significant difference in the intensity of postrotatory nystagmus between the Fresnel-based device with 4-fold magnification (37.3 ± 17.9°/s) and the Frenzel goggles (39.0 ± 18.3°/s). There was also no significant difference between the intensity of peripheral vestibular spontaneous nystagmus in the patients with acute vestibular neuritis. The Fresnel-based device can be easily applied.
Conclusion:
For suppression of nystagmus, the new Fresnel-based device or so-called M glasses is not inferior to Frenzel goggles. Doctors can carry it in their pocket, it is inexpensive, and easy to handle and to fix to the patient's nose so that it can be used in daily practice for the bedside examination.
Classification Of Evidence:
This study provides Class III evidence that, in subjects with nystagmus, a Fresnel-based device identifies a similar intensity of nystagmus as that identified by Frenzel goggles.
