Abstract
Background
Caloric nystagmus contains not only a horizontal component but also vertical and torsional components. Several researchers considered that their origins are the posterior and superior semicircular canals. If the right superior canal receives caloric stimulation in the left-ear-down 40° position, an endolymphatic flow occurs in the direction of gravity in the long arm and induces ampullofugal cupular deflection. As a result, the direction of the vertical component of nystagmus should be downward (toward the lower eyelid), and the direction of the torsional component should be rightward.
Purpose
The purpose of this study is to confirm the hypothesis that the superior semicircular canal receives caloric stimulation.
Methods
The subjects were 10 healthy humans. The right ear was stimulated using iced water. Each subject was kept in a left-ear-down 40° position for 60 seconds and then repositioned to a supine position. Nystagmus was analyzed by 3-dimensional video-oculography.
Results
In the left-ear-down 40° position, the direction of quick phase of the horizontal component was leftward in all subjects. Eight subjects exhibited a vertical component, and the direction was upward (toward the upper eyelid). Six subjects showed a torsional component, and the direction was leftward (the superior pole of the eyeball moved toward the left ear of the subject in a quick phase). These findings contradict the hypothesis.
Conclusion
Caloric stimulation does not reach the superior canal; therefore, caloric testing cannot be used to evaluate the function of superior canal.
1
Introduction
The advantage of caloric testing is that it provides lateralizing information not available from any other vestibular laboratory test. Most commonly, physicians use electronystagmography and measure the slow-phase velocity of the horizontal component of caloric nystagmus to quantify the response. After the accomplishment of 3-dimensional video-oculography, Yagi et al found that caloric nystagmus contains both vertical and torsional components. Several researchers considered that their origins are the posterior and superior semicircular canals . However, there is a possibility that vertical and torsional components are derived from the horizontal semicircular canal.
To confirm the hypothesis that the superior semicircular canal receives caloric stimulation, we performed 3-dimensional analysis of caloric nystagmus in the left-ear-down 40° position, which makes the right superior canal earth vertical. The accuracy of video-oculography is equivalent to that of scleral search coil system .
2
Materials and methods
Ten healthy humans (7 males, 3 females, aged 24–51 years) without oculomotor or vestibular abnormalities were tested. All subjects gave informed consent to participate in the study. We slowly poured 1 mL of iced water (6°C) into the right external auditory canal in a left-ear-down 90° position using a small syringe, taking 20 seconds. Each subject was rotated to a left-ear-down 40° position to bring the right superior canal into the earth vertical plane ( Fig. 1 ). Sixty seconds later, the subject was repositioned to a supine position and stayed there until the nystagmus stopped.
The experiment was performed in the dark with the subjects’ eyes open using an infrared charge-coupled device camera. Caloric nystagmus was recorded and converted to digital data. Using ImageJ (a public domain, Java-based image processing program developed at the National Institutes of Health) and a Macintosh computer (Mac OS 10.6.2), 3-dimensional video-oculography was performed. For analysis of horizontal and vertical components, the XY center of the pupil was calculated. For analysis of the torsional component, the whole iris pattern, which was rotated in steps of 0.1°, was overlaid with the same area of the next iris pattern, and the angle at which both iris patterns showed the greatest match was calculated . Maximum slow-phase velocity (MSV) of the 3 components and duration of nystagmus were measured using a video-oculography.
2
Materials and methods
Ten healthy humans (7 males, 3 females, aged 24–51 years) without oculomotor or vestibular abnormalities were tested. All subjects gave informed consent to participate in the study. We slowly poured 1 mL of iced water (6°C) into the right external auditory canal in a left-ear-down 90° position using a small syringe, taking 20 seconds. Each subject was rotated to a left-ear-down 40° position to bring the right superior canal into the earth vertical plane ( Fig. 1 ). Sixty seconds later, the subject was repositioned to a supine position and stayed there until the nystagmus stopped.
The experiment was performed in the dark with the subjects’ eyes open using an infrared charge-coupled device camera. Caloric nystagmus was recorded and converted to digital data. Using ImageJ (a public domain, Java-based image processing program developed at the National Institutes of Health) and a Macintosh computer (Mac OS 10.6.2), 3-dimensional video-oculography was performed. For analysis of horizontal and vertical components, the XY center of the pupil was calculated. For analysis of the torsional component, the whole iris pattern, which was rotated in steps of 0.1°, was overlaid with the same area of the next iris pattern, and the angle at which both iris patterns showed the greatest match was calculated . Maximum slow-phase velocity (MSV) of the 3 components and duration of nystagmus were measured using a video-oculography.
3
Results
Data on the 10 subjects are shown in Table 1 .
| Subject | Age (y) | Left-ear-down 40° | Supine | Duration (s) | ||||
|---|---|---|---|---|---|---|---|---|
| H (°/s) | V (°/s) | T (°/s) | H (°/s) | V (°/s) | T (°/s) | |||
| 1 | 24 | 12 | 6 (U) | 3 | 37 | 5 (U) | 16 | 280 |
| 2 | 29 | 15 | 5 (U) | 8 | 32 | 0 | 0 | 183 |
| 3 | 31 | 5 | 3 (U) | 3 | 19 | 0 | 0 | 227 |
| 4 | 32 | 22 | 6 (U) | 0 | 33 | 9 (U) | 0 | 181 |
| 5 | 33 | 15 | 7 (U) | 6 | 28 | 5 (U) | 6 | 194 |
| 6 | 41 | 11 | 5 (U) | 4 | 15 | 4 (U) | 4 | 190 |
| 7 | 42 | 8 | 11 (U) | 4 | 34 | 7 (U) | 6 | 248 |
| 8 | 46 | 12 | 4 (U) | 0 | 45 | 0 | 0 | 231 |
| 9 | 49 | 16 | 0 | 0 | 24 | 0 | 8 | 198 |
| 10 | 51 | 3 | 0 | 0 | 8 | 0 | 0 | 224 |
| Mean | 37.8 | 11.9 | 4.7 | 2.8 | 27.5 | 3 | 4 | 216 |
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