The authors developed thin, light, Fresnel-based glasses for examining patients with nystagmus and found that for suppression of nystagmus, the new device is not inferior to Frenzel goggles. Doctors can carry them in a pocket and they are inexpensive and easy to handle and place on a patient's nose, making them useful for bedside exams in daily practice.
The first aim of this study was to develop a new type of examination tool for nystagmus to overcome the limitations of Frenzel goggles based on thin Fresnel lenses that were described by the French physicist Augustin-Jean Fresnel in 1822. He developed lighter and smaller glasses based on an optical system in which a series of small base-in prisms replaced a large convex lens.
Also known as M glasses, the Fresnel lenses developed by the authors have short focal length and weigh significantly less than the Freznel goggles (6 grams vs. 500 grams).
The authors compared visual-fixation suppression of postrotatory nystagmus with Frenzel goggles and the new Fresnel lenses (with 2- and 4-fold magnification) in 13 healthy subjects. They also compared the intensity of peripheral vestibular spontaneous nystagmus in 6 patients with acute vestibular neuritis with the Frenzel goggles and the Fresnel-based device with 4-fold magnification.
They found no significant difference in the intensity of postrotatory nystagmus between the Fresnel-based device with 4-fold magnification and the Frenzel goggles. There also was no significant difference between the intensity of peripheral vestibular spontaneous nystagmus in patients with acute vestibular neuritis.
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.
They note that in addition to its much lighter weight and smaller size, the Fresnel-based device also does not require a power supply, allowing it to be carried in a pocket; can be fastened to the patient's nose, allowing the examiner to have both hands free; and also costs significantly less than the goggles ($60 compared to $500 to $800).
The authors conclude that in clinical practice, the Fresnel-based lenses should be used in all patients with vertigo, dizziness, postural imbalance and oscillopsia.