Clinical examination of eye movements and nystagmus allows the diagnosis of possible brainstem- or cerebellar lesions in several cases of dizziness and can differentiate among peripheral, central oculomotor, and vestibular lesions [5]. Dizziness is a common presentation in the emergency department, and nystagmus evaluation and a definition of its characteristics by the emergency physician are important for determining acute dizziness. One of the crucial clinical signs for differentiating between acute peripheral and central vertigo is the suppression of spontaneous nystagmus by visual fixation [6]. However, Kerber et al. examined emergency department medical records and demonstrated that despite frequent nystagmus assessment recordings in patients presenting with acute vertigo, the details generally do not allow meaningful inferences. Furthermore, the effects of the fixation removal were not mentioned. The recorded descriptions often conflict during a peripheral vestibular diagnosis [7]. The Frenzel goggles were not used in the emergency department, despite their ruggedness and portability. The underutilization of nystagmus information may be attributed to the fact that medical education programs do not incorporate up-to-date training of nystagmus assessment into their curricula. Furthermore, medical students perceive neurology as the most difficult subspecialty because of the complicated and difficult clinical examination [8]. Recently, most neuro-otology clinics and specialists have used infrared video nystagmus goggles for greater precision and permanent measurable records [3]. Therefore, students and residents may perceive the distinct nystagmus on the infrared video recordings observed in the lecture to be relatively different from that observed in the emergency department using the Frenzel goggles or the naked eye. Thus, students should be trained to observe nystagmus using the Frenzel goggles or a comparable tool.
In this study, we proposed a medical education practice of nystagmus observation for students using a new portable Fresnel magnifying loupe that is inexpensive and easy to operate. The nystagmus counts observed with the new loupe was greater than that observed with the naked eye and comparable to that observed with the Frenzel goggles. Because this study was conducted with physical therapy and speech-language and hearing therapy students, even residents, physicians, and medical staff unfamiliar with nystagmus findings could easily observe nystagmus with the new loupe.
Furthermore, students could use this loupe for HINTS training (Fig. 5). Students can perform a cover test and Test of Skew upon storing the lens in a cover (Fig. 5b). The HINTS exam has a higher sensitivity than hyperacute magnetic resonance imaging in diagnosing posterior circulation stroke in patients presenting with acute vestibular syndrome [2]. However, Mahmud et al. noted that the HINTS was sometimes inappropriately applied or incorrectly interpreted in the emergency department of a large tertiary hyperacute stroke center [9]. Therefore, adequate HINTS training should be provided in student practice and the developed loupe will prove useful in this context.
Strupp et al. created Fresnel-based devices with 2× (134-mm focal distance) and 4× (63-mm focal distance) magnifications and compared them with the Frenzel goggles. The maximum slow-phase velocity of the postrotatory nystagmus with the 4× Fresnel-based device was similar to that with the Frenzel goggles; however, the maximum slow-phase velocity was significantly lower with the 2× device [10]. Their glasses weighed 6 g and could be fastened to the participant's nose such that both the hands of the examiner remained unoccupied. Our loupe is more hygienic because it does not contact the participant, although the examiner must secure it in place using one hand.
Yeolekar et al. reported on the usefulness of modified Google Cardboard as the Frenzel goggles, which are superior to the naked eye in identifying spontaneous nystagmus. Although it is a cheaper alternative, modified Google Cardboard should be used in a well-lit room, as it does not have inbuilt lighting [11]. Our loupe can be used with natural light and does not require a power supply.
One advantage of the new loupe is that it does not contact the face; therefore, there is less concern about clouding [10]. The Frenzel goggles cover the eyes in close contact with the participant's face. Further, the participant’s body heat causes occasional lens clouding when the room temperature is low.
The major advantages of the Fresnel magnifying loupe are as follows: First, it weighs only 24 g, is thin, and can be stored in a cover to prevent damage to the lens, thus making it portable. Second, it does not require a power supply and can be observed under normal room light. Third, the device is excellent for infection control because it can be used without contact with the participant and can be disinfected by wiping it with alcohol. Their simple structure is inexpensive, compared with the conventional Frenzel goggles. Further, it can be prepared for the practical use by numerous students.
Limitations
This study was designed for student practice; thus, we used an office swivel chair for the rotational stimulation. Therefore, the rotational stimulus may not be constant. In addition, the nystagmus counts was used for its evaluation. To improve the accuracy of the comparison, constant programmed acceleration stimulation should be performed in the rotary chair in the clinical examination. In addition, the intensity of nystagmus should be evaluated by the maximum slow-phase velocity by using electronystagmography. To confirm the usefulness of the loupe in clinical examinations, e.g., in the emergency department, clinicians are required to compare spontaneous nystagmus in patients using the loupe with those using other tools. In this case, comparisons were made at the maximum slow-phase velocity.